{"id":"9a17ec4d-457c-4464-a6c8-f873f9548bd5","arxiv_id":"1908.03667","paper_version":2,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":3,"one_line_summary":"High-pressure optical measurements show that the mid-infrared hybridization peak grows and shifts up in energy in CeRhIn5, but shrinks and shifts down in YbNi3Ga9.","lead":"This paper measures how the optical response of two heavy-fermion compounds, CeRhIn5 and YbNi3Ga9, changes under pressure up to 10 GPa. It finds opposite behavior: pressure strengthens the hybridization feature in CeRhIn5 while weakening it in YbNi3Ga9, which tests ideas about electron-hole symmetry in f-electron materials.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The claim of opposite pressure evolutions is supported; the weakest link is the interpretation of YbNi3Ga9's diminishing mIR peak as reduced V-tilde, which uses Eq. (2) with an unmeasured f-level shift and depends on a constrained Drude-Lorentz fit at 10 GPa.","rationale":"The reader's weakest assumption is essentially the one I identify: the interpretation of YbNi3Ga9's mIR peak rests on an unmeasured f-level shift argument. I agree partially, but the reader phrases the concern as 'if this were wrong, the diminishing mIR peak could have a different origin,' whereas my stress-test adds a concrete procedural concern: the 10 GPa data point that anchors the diminuition is the least constrained by the fit, and the Appendix explicitly says the mIR peak is not well resolved from the Drude component at that pressure. The load-bearing nature is that the headline conclusion about YbNi3Ga9, and hence the e-h symmetry contrast, depends on interpreting the low-energy evolution as a genuine shift and loss of mIR spectral weight, not merely a re-partitioning of spectral weight between Drude and Lorentz oscillators in an underconstrained fit. This does not overturn the paper, but it strengthens the need for the CONDITIONAL verdict. I see no internal inconsistency in the raw spectral evolution shown in Fig. 5; the qualitative opposite tendencies are visible in the data. The weakness is entirely in the quantitative interpretation step, so the verdict should remain CONDITIONAL rather than being upgraded or rejected.","tokens_in":15374,"tokens_out":1621,"duration_ms":16109,"concrete_test":"Re-analyze the YbNi3Ga9 low-temperature sigma(omega) at 6 and 10 GPa with fixed Drude parameters anchored to measured dc sigma0 and with the high-energy Lorentz background held fixed, allowing only the mIR oscillator set to vary; then repeat allowing the Drude scattering rate to vary over a range consistent with the DC conductivity uncertainty. If the fitted EmIR and the mIR spectral weight at 10 GPa change by more than the reported P-trend (0.18 to 0.10 eV), the claim that the mIR peak shifts to lower energy and diminishes is not robust.","verdict_should_be":"CONDITIONAL","load_bearing_attack":"The central claim of opposite pressure evolutions is well supported by the raw spectra in Fig. 5, so I do not dispute the qualitative experimental finding. The load-bearing concern is the specific interpretation of YbNi3Ga9's diminishing mIR peak: Section III.C and Eq. (1) interpret EmIR as tracking 2V-tilde, and attribute the decrease of EmIR to |EF - ef| increasing faster than |V|^2 in Eq. (2). The f-level shift is asserted via a generic argument (footnote 63 and Ref. 61), not measured for YbNi3Ga9, and the paper itself acknowledges that Jcf may either increase or decrease; the conclusion relies entirely on the observed EmIR decrease. Moreover, the 10 GPa point, which anchors the 'diminished and merged with Drude' conclusion, is the hardest to fit: the Appendix states the mIR peak is 'not well resolved from the Drude component any more,' so the fitted EmIR and SW at 10 GPa are strongly model-dependent. The paper does not report error bars or robustness checks for these fits, and no data deposit is provided to allow independent testing. A valence crossover, enhanced scattering, or a change in the Drude-Lorentz decomposition could also produce a weakening and apparent downshift of the mIR feature; the claim that this reflects reduced renormalized hybridization would then be weakened, although the qualitative contrast with CeRhIn5 would still stand.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper reports optical conductivity measurements of CeRhIn5 and YbNi3Ga9 under external pressures up to 10 GPa and at low temperatures (6–8 K). The central empirical finding is that the mid-infrared (mIR) peak evolves oppositely in the two compounds: in CeRhIn5 it develops with pressure and shifts to higher energy, whereas in YbNi3Ga9 it weakens and shifts to lower energy, nearly merging with the Drude component at 10 GPa. The authors interpret these trends as opposite pressure dependencies of the effective c-f hybridization and discuss them within the electron-hole symmetry picture between Ce and Yb compounds.","tokens_in":15704,"tokens_out":3426,"duration_ms":38136,"significance":"If the interpretation holds, the paper provides valuable new high-pressure optical data that constrain how c-f hybridization evolves across the Ce/Yb electron-hole asymmetry. The raw spectra in Fig. 5 give direct, model-independent evidence of the contrasting qualitative trends, and the placement of the new data points on the existing universal relation of Ref. 10 is a useful empirical test rather than a circular fit. The high-pressure DAC optical experiments to 10 GPa are technically demanding, and the comparison between a Ce and a Yb compound in the same pressure range is instructive. The main weakness is that the quantitative YbNi3Ga9 trajectory, and especially the interpretation of the diminishing mIR peak as a decrease in renormalized hybridization, rests on fit-dependent quantities and an unmeasured f-level shift.","major_comments":[{"comment":"The quantitative evolution of the mIR peak in YbNi3Ga9, most importantly the 10 GPa point that anchors the 'merged with Drude' conclusion, is obtained from Drude-Lorentz fitting in a regime where the text itself states that the mIR peak is 'not well resolved from the Drude component any more.' No uncertainties or robustness checks are reported for the fitted EmIR, FWHM, and SW values. Please provide estimates of fit uncertainty, for example by varying the number of Lorentz oscillators, changing the Drude constraints, or trying alternative decompositions. As written, the quantitative downshift and reduced spectral weight at 10 GPa cannot be distinguished from decomposition ambiguity.","section":"Appendix and Fig. 4(d)"},{"comment":"The inference that the decreasing EmIR of YbNi3Ga9 reflects a decrease of the renormalized hybridization V~ assumes that |EF - εf| increases with pressure faster than |V|^2. This f-level shift is not measured for YbNi3Ga9; footnote 63 and Ref. 61 provide a generic electrostatic argument, not material-specific data. The paper should explicitly label this as a plausible interpretation rather than a demonstrated conclusion, and discuss alternative origins of the weakening and apparent downshift of the mIR peak, such as a valence crossover, enhanced scattering, or changes in the Drude-Lorentz decomposition. This issue is load-bearing because the paper's central statement about 'opposite pressure evolutions of f electron hybridized states' relies on the assignment of the YbNi3Ga9 mIR peak evolution to a reduced V~.","section":"Section III.C, Eq. (2)"}],"minor_comments":[{"comment":"The text contains a typo: 'Kramres-Kronig' should be 'Kramers-Kronig'.","section":"Section II"},{"comment":"The two-peak structure of the YbNi3Ga9 mIR feature at 3 and 6 GPa is described in the main text, and the center-of-mass definition of EmIR is given only in the Appendix. This definition and the criterion for using more than two Lorentz oscillators should be stated in the main text where the fit results are first discussed.","section":"Fig. 4(c), Fig. 4(d)"},{"comment":"The interpolation across the 0.23–0.3 eV range caused by diamond absorption is mentioned in the figure captions and footnote 49, but a sensitivity test or illustrative comparison showing that the interpolation does not affect the mIR peak parameters would increase confidence in the quantitative fits.","section":"Fig. 3(b) and Fig. 4(b)"},{"comment":"The newly added data points are described as red, but the caption does not specify how they are distinguished in grayscale printing; using distinct symbols in addition to color would improve accessibility.","section":"Fig. 1 caption"}],"recommendation":"major_revision","confidential_remarks":"The qualitative experimental contrast in Fig. 5 is convincing and should be published after revision. The main risk is the interpretation of the YbNi3Ga9 mIR peak as a direct measure of decreasing V~, which is based on an unmeasured f-level shift and fit-dependent 10 GPa data. The authors should be asked to add uncertainty/robustness analysis and to moderate the interpretive claims, not to change the experimental message."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Dear colleague,\n\nThe core experimental result is new and it is right: in CeRhIn5 the mid-infrared peak develops and shifts up with pressure (roughly 70 to 90 meV from 2 to 8 GPa), while in YbNi3Ga9 the mIR peak, strong at ambient pressure, shifts down and fades into the Drude tail by 10 GPa. One can see that contrast directly in Fig. 5 without trusting any fitting. So the main claim of opposite pressure evolutions of the renormalized hybridization is well supported.\n\nWhat the paper does well: the measurements are first of their kind for these compounds, the authors add their new EmIR points to the existing universal relation and show Ce moves up-right and Yb moves down-left, and they are honest about what does not fit the simple e-h symmetry picture (peak width, magnitude of shift, the two-peak structure in Yb). They also explicitly say the origin of the two peaks is unclear. This is a genuine test of the e-h symmetry idea, not a circular fit.\n\nSoft spots, in proportion. No uncertainties are reported for EmIR, FWHM, or SW from the multi-oscillator Drude-Lorentz fits. That matters for quantitative use. At 10 GPa in YbNi3Ga9 the Appendix admits the mIR peak is not well resolved from the Drude component, so the fitted EmIR and SW at that point are model-dependent. The qualitative weakening is already clear at 6 GPa, so the paper's central point does not rest on the 10 GPa fit alone. The interpretation of Yb's downshift as a decrease in V-tilde uses Eq. (2) with an f-level shift that is not measured for YbNi3Ga9 (footnote 63 and Ref. 61). The authors frame the conclusion as \"consistent with\", which is the right register; it is a plausible scenario rather than a demonstrated one. No public data deposit, but that is a minor issue.\n\nWho this is for: the heavy-fermion and strongly correlated electron community. The paper deserves a serious referee. I would ask the referee to require error bars or robustness checks on the fit parameters and an explicit statement about the reliability of the 10 GPa Yb point. With those, it would be publishable as strong experimental work.\n\nRecommendation: accept for peer review.","headline":"New high-pressure optics data with an opposite mIR-peak trend across a Ce/Yb pair; the qualitative claim holds, but the Yb interpretation leans on an unmeasured f-level shift and fit-dependent points.","tokens_in":16263,"tokens_out":3930,"would_cite":true,"duration_ms":39022,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":["75.30.Mb","74.70.Tx","74.62.Fj","78.30.-j"],"model":"deepseek-v4-flash","headline":"Optical conductivity under pressure shows CeRhIn$_5$ and YbNi$_3$Ga$_9$ develop opposite f-electron hybridization trends.","keywords":["optical conductivity","mid-infrared peak","c-f hybridization","heavy fermion","intermediate valence","CeRhIn5","YbNi3Ga9","electron-hole symmetry"],"falsifier":"Measure YbNi$_3$Ga$_9$'s valence and $f$-level position relative to the Fermi energy (for example, by X-ray absorption or photoemission) across 0-10 GPa; if $|E_F-\\varepsilon_f|$ does not increase faster than $|V|^2$, or if the declining mid-infrared peak energy loses its correlation with an independently measured Kondo scale, the electron-hole symmetry explanation would be falsified.","tokens_in":15176,"feed_emoji":"🔬","tokens_out":14742,"duration_ms":129996,"temperature":0.7,"pith_summary":"This paper measures optical conductivity of CeRhIn$_5$ and YbNi$_3$Ga$_9$ under pressures up to 10 GPa and at temperatures down to 6 K, trying to show how their $f$-electron hybridization responds to pressure. In CeRhIn$_5$ a mid-infrared absorption peak appears and shifts upward in energy, from roughly 70 meV at 2 GPa to about 90 meV at 8 GPa, signaling stronger hybridization between conduction and $f$ electrons. In YbNi$_3$Ga$_9$ the same kind of peak, already strong at ambient pressure, shifts downward and fades until it nearly merges with the Drude free-carrier response at 10 GPa, indicating effective hybridization that weakens under pressure. The authors attribute both trends to the electron-hole symmetry between Ce$^{3+}$ ($f^1$) and Yb$^{3+}$ ($f^{13}$) combined with ionic-radius effects, and they locate the pressure evolution on a known universal relation between peak energy and hybridization strength. If correct, the results make optical spectroscopy a direct probe of pressure-tuned localization and test how far the Ce-Yb electron-hole analogy extends.","feed_headline":"Pressure makes CeRhIn5 and YbNi3Ga9 hybridize in opposite directions","feed_subtitle":"Optical spectra show CeRhIn5's f-electron mixing grows with pressure while YbNi3Ga9's fades.","key_machinery":"The central object is the mid-infrared (mIR) peak in optical conductivity, interpreted as an optical excitation across renormalized $c$-$f$ hybridized bands. The load-bearing identity is $E_{\\rm mIR}\\simeq 2\\tilde{V}\\simeq\\sqrt{T_K W}$, which ties the peak position to the renormalized $c$-$f$ hybridization $\\tilde{V}$, the Kondo temperature $T_K$, and the conduction bandwidth $W$; a second identity, $J_{cf}\\simeq |V|^2/|E_F-\\varepsilon_f|$, links the effective exchange to the bare hybridization $V$ and the $f$-level position. Pressure enters through the ionic-radius/electron-hole picture: it moves the Ce $f$ level toward $E_F$ and the Yb $f$-hole level away from $E_F$. The mIR peak's energy, width, and spectral weight are then used as a direct optical readout of whether pressure localizes or delocalizes the $f$ electrons.","core_discovery":"The central claim is that the pressure evolution of the mid-infrared peak in optical conductivity is opposite for the two compounds. In CeRhIn$_5$ the mIR peak develops with pressure and moves from roughly 70 meV at 2 GPa to about 90 meV at 8 GPa, while its width and spectral weight grow; on the standard reading $E_{\\rm mIR}\\simeq 2\\tilde{V}$, this is a pressure-driven increase of the renormalized $c$-$f$ hybridization, moving the material from nearly localized toward intermediate-valence behavior. In YbNi$_3$Ga$_9$ the well-developed mIR peak at ambient pressure ($E_{\\rm mIR}\\approx 0.18$ eV) shifts downward and weakens with pressure, nearly merging with the Drude component at 10 GPa, which the paper takes as a decrease of effective hybridization despite the expected increase of bare hybridization. The proposed mechanism is the ionic-radius and electron-hole argument: pressure raises the Ce 4$f$ level toward $E_F$, so $J_{cf}\\simeq |V|^2/|E_F-\\varepsilon_f|$ grows, while it raises the Yb 4$f$-hole level away from $E_F$, so the denominator wins and $J_{cf}$ falls. The two materials therefore move in opposite directions on the universal relation between mIR peak energy and a hybridization measure.","pith_inferences":["A testable extension of the electron-hole argument is that other Yb-based intermediate-valence compounds, such as YbCu$_2$Ge$_2$ and YbAl$_2$, should show a similar pressure-induced downturn of their mIR peak energy; measuring their optical conductivity under pressure would check whether the Yb behavior is generic.","Because the paper does not directly measure the Yb $f$-level position, an experiment tracking that level relative to the Fermi energy under pressure (for example, by photoemission or resonant X-ray emission) could confirm that it moves away faster than the raw hybridization grows; if not, the weakening-hybridization reading would need revision.","The model implies that YbNi$_3$Ga$_9$'s mIR peak energy should keep decreasing or saturate beyond 10 GPa as long as the $f$-hole level outruns the growing bare hybridization; a turnaround at higher pressure would signal that the bare hybridization term eventually dominates."],"forward_implications":["For CeRhIn$_5$, the low-temperature normal state is tuned by pressure from weakly hybridized to strongly hybridized, with the mIR peak energy rising from 70 to 90 meV, so the electronic structure that hosts the quantum critical and superconducting behavior is not fixed.","For YbNi$_3$Ga$_9$, the effective $c$-$f$ hybridization decreases with pressure even though atomic overlap increases, consistent with the measured valence increase and the appearance of antiferromagnetic order above the critical pressure near 9 GPa.","The pressure points of both compounds fall on the same universal relation between mIR peak energy and hybridization measure, with CeRhIn$_5$ moving to higher hybridization energy and YbNi$_3$Ga$_9$ to lower.","At 10 GPa YbNi$_3$Ga$_9$ still shows a residual mIR component with sizable spectral weight, so some hybridization persists even in the more localized regime.","The observed asymmetry in peak broadening and in the size of the energy shift shows that the simple electron-hole symmetry picture is only qualitative for these two materials."],"supporting_citations":[{"why":"These references supply the renormalized $c$-$f$ hybridized band model and the relation between mid-infrared peak energy, Kondo temperature, and conduction bandwidth used to interpret the peak.","marker":"18–20"},{"why":"This reference establishes the universal relation between mid-infrared peak energy and the hybridization measure that the new pressure points are placed on.","marker":"10"},{"why":"These references provide the ionic-radius and electron-hole symmetry arguments for how pressure shifts Ce and Yb valence and hybridization.","marker":"23–26"},{"why":"This reference gives YbNi$_3$Ga$_9$'s valence and resistivity under pressure, including the antiferromagnetic transition above about 9 GPa, anchoring the interpretation of the optical data.","marker":"36"},{"why":"This reference supplies specific-heat coefficients of YbNi$_3$Ga$_9$ at high pressure, used to plot its peak energy on the universal relation.","marker":"37"},{"why":"This reference documents CeRhIn$_5$'s antiferromagnetism and specific-heat coefficient at ambient pressure, providing the baseline for the pressure evolution.","marker":"27"},{"why":"This reference's resistivity data under pressure are used to infer that CeRhIn$_5$'s hybridization is much stronger at 8 GPa.","marker":"28"},{"why":"This reference provides the exchange expression used to argue why Yb's effective exchange can decrease under pressure even when the bare hybridization increases.","marker":"62"}],"fun_headline_variants":["Pressure drives Ce and Yb f-electron hybridization opposite ways","Optical probe shows pressure splits Ce and Yb hybridization trends","CeRhIn5 and YbNi3Ga9: pressure flips hybridization direction","Pressure sends Ce and Yb hybrids in opposite directions","Same pressure, opposite f-electron hybridization in Ce, Yb compounds"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The argument depends on the assumption that the mid-infrared peak's energy directly measures the renormalized $c$-$f$ hybridization and that in YbNi$_3$Ga$_9$ pressure pushes the $f$-hole level away from the Fermi energy faster than it increases the raw hybridization; if the peak simply faded because of a valence crossover or a band-structure effect, the opposite-hybridization conclusion would not follow.","fun_headline_variants_meta":{"raw":{"variants":["Pressure drives Ce and Yb f-electron hybridization opposite ways","Optical probe shows pressure splits Ce and Yb hybridization trends","CeRhIn5 and YbNi3Ga9: pressure flips hybridization direction","Pressure sends Ce and Yb hybrids in opposite directions","Same pressure, opposite f-electron hybridization in Ce, Yb compounds"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000743,"raw_usage":{"total_tokens":3420,"prompt_tokens":1154,"completion_tokens":2266,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":770,"completion_tokens_details":{"reasoning_tokens":2177}},"tokens_in":770,"tokens_out":2266,"duration_ms":15519,"temperature":1.0,"reasoning_tokens":2177,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-14T14:06:25.366754+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure YbNi$_3$Ga$_9$'s valence and $f$-level position relative to the Fermi energy (for example, by X-ray absorption or photoemission) across 0-10 GPa; if $|E_F-\\varepsilon_f|$ does not increase faster than $|V|^2$, or if the declining mid-infrared peak energy loses its correlation with an independently measured Kondo scale, the electron-hole symmetry explanation would be falsified.","supporting_citations":[{"cited_title":"Okamura, T","cited_arxiv_id":null,"evidence_quote":"This reference establishes the universal relation between mid-infrared peak energy and the hybridization measure that the new pressure points are placed on."},{"cited_title":"Matsubayashi, T","cited_arxiv_id":null,"evidence_quote":"This reference gives YbNi$_3$Ga$_9$'s valence and resistivity under pressure, including the antiferromagnetic transition above about 9 GPa, anchoring the interpretation of the optical data."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"This reference supplies specific-heat coefficients of YbNi$_3$Ga$_9$ at high pressure, used to plot its peak energy on the universal relation."},{"cited_title":"Hegger, C","cited_arxiv_id":null,"evidence_quote":"This reference documents CeRhIn$_5$'s antiferromagnetism and specific-heat coefficient at ambient pressure, providing the baseline for the pressure evolution."},{"cited_title":"Muramatsu, N","cited_arxiv_id":null,"evidence_quote":"This reference's resistivity data under pressure are used to infer that CeRhIn$_5$'s hybridization is much stronger at 8 GPa."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"This reference provides the exchange expression used to argue why Yb's effective exchange can decrease under pressure even when the bare hybridization increases."}],"review_version":1}