强关联电子系统超导电性的高压研究

郭静; 孙力玲

doi:10.11858/gywlxb.20210889

强关联电子系统超导电性的高压研究

doi: 10.11858/gywlxb.20210889

郭静^{1, 2,},
孙力玲^{1, 2, 3,*, ,}

1.
中国科学院物理研究所, 北京凝聚态物理国家研究中心, 北京　100190
2.
松山湖材料实验室, 广东东莞　523808
3.
中国科学院大学, 北京　100049

基金项目: 国家自然科学基金（U2032214，12122414）；国家重点基础研究发展计划（2017YFA0302900）；中国科学院B类先导项目（XDB25000000）

详细信息

作者简介:
郭　静（1985－），女，博士，副研究员，主要从事高压下超导材料和其他电子关联材料的物性研究. E-mail：jguo@iphy.ac.cn

通讯作者:
孙力玲（1958－），女，博士，研究员，主要从事高压-低温-磁场条件下超导及其他量子材料的物态和物性研究. E-mail：llsun@iphy.ac.cn

中图分类号: O521.2
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出版历程
- 收稿日期: 2021-10-11
- 修回日期: 2021-11-08

High Pressure Studies on Superconductivity of Strongly Correlated Electron Systems

GUO Jing^{1, 2
,},
SUN Liling^{1, 2, 3,*
, ,}

1.
Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
2.
Songshan Lake Materials Laboratory, Dongguan 523808, Guangdong, China
3.
University of Chinese Academy of Sciences, Beijing 100049, China

摘要

摘要: 具有强关联电子特性的凝聚态系统中，电子间的强关联性主导系统的宏观量子特性。这类系统具有电荷、自旋、轨道、晶格及拓扑等多重自由度，这些自由度强烈耦合，产生复杂的多体相互作用，导致系统出现丰富奇异的量子现象，如非常规超导电性、庞磁电阻、金属-绝缘体转变、拓扑量子相变等。其中，非常规超导体的研究于近几十年取得了不少进展，例如发现了铜氧化物高温超导电性和铁基超导体，然而导致非常规超导电性的原因，尤其是对高温超导电性的机理认识目前尚不清楚，非常规超导机理一直是凝聚态物理研究领域中最具挑战性的问题之一。为此，简要介绍了近年来我们通过高压实验手段在重费米子超导体、铜氧化物超导体和铁基超导体这3类主要的非常规超导体研究中取得的进展、发现的新现象以及反映的新物理机理，包括磁性和超导电性的演化关系、价态变化对超导电性的影响、铜氧化物的普适压力相图等，旨在提供非常规超导体在高压研究方面的一些实验新进展，以期为更好地理解非常规超导的微观机理提供压力维度下的一些信息。
- 高压 /
- 强关联电子系统 /
- 超导电性 /
- 磁有序
Abstract: The coexistence and interplay between spin, charge, orbital and lattice in electron correlated systems give rise to many interesting quantum phenomena, including unconventional superconductivity, colossal magnetoresistance, metal-insulator transition, topological phase transition, etc. While, as one of the most important issues in condensed matter physics, the mechanism of the unconventional high temperature superconductivity is still unclear up to now. In this paper, we report some new phenomena/physics obtained from our high pressure studies on three typically unconventional superconductors—heavy fermion superconductor, cuprate high temperature superconductor and iron-based superconductor, which include the correlation between magnetism and superconductivity, the influence of valence change on superconductivity, the discovery of superconductivity reemerging, the bi-critical points, and the universal transition from superconducting to insulating-like states, etc. These high-pressure experimental results on the unconventional superconductors are expected to provide useful information for a better understanding on the unconventional superconducting mechanism.
- high pressure /
- strongly correlated electron systems /
- superconductivity /
- magnetic order

HTML全文

图 1 (a) CeRhGe₃的压力-温度相图（橄榄色的空心正方形是从文献[56]中选取的转变温度T_N1）；(b) CeTX₃化合物的$T_{\rm{c}}^{\rm{max}} $与相应临界体积V_crit之间的关系^[59]

Figure 1. (a) Pressure-temperature phase diagram of CeRhGe₃, in which the olive hollow square is the transition temperature T_N1 adopted from Ref.[56]; (b) relation between $T_{\rm{c}}^{\rm{max}} $ and the critical volume V_crit for CeTX₃^[59]

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图 2 (a) CeRhGe₃和CeIrGe₃的超导转变温度T_c和反铁磁转变温度T_N随压力（p）的变化（黄色圆点和紫色圆点分别代表CeRhGe₃的T_N和T_c；黑色空心圆和黑色实心圆分别代表CeIrGe₃ 的T_N和T_c ^[51]）； (b) 室温时不同压力下CeRhGe₃中Ce-LⅢ的X射线吸收光谱；(c) CeRhGe₃中Ce的平均价态随压力的变化^[66]

Figure 2. (a) Evolutions of the superconducting transition temperatures T_c and the AFM transition temperatures T_N with pressure p for CeRhGe₃ and CeIrGe₃, the open and filled black circles represent the T_N and the T_c of CeIrGe₃^[51]; (b) Ce-LⅢ X-ray absorption spectra of CeRhGe₃ at room temperature for various pressures; (c) pressure dependence of the mean valence of Ce ions in CeRhGe₃^[66]

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图 3 CeRhGe₃在p_c（21.5 GPa）附近时低温电阻的标度化分析：(a) 2～10 K时等温电阻（R^*=R−R₀）随压力的变化（红色正方形代表p_c处的R^*下降50%时的压力p_vc和温度，红线代表p_vc随温度变化的关系，外延至零温得到一阶价态相变的临界终点对应的压力p_cr）；(b) 归一化等温电阻R_nor（R_nor = [R^*−R^*(p_vc)]/R^*(p_vc)）随压力的变化（红色正方形对应图3(a)中的红色正方形）；(c) 归一化等温电阻在p_vc时的斜率（$\,\chi$ = |dR_nor/dp|_pvc）随温度的变化（红色虚线代表Curie-Weiss拟合，得到T_cr = −20 K）；(d) 归一化等温电阻作为广义距离h/$ \theta$的函数时的塌缩行为（h = (p− p_vc)/p_vc，$\theta $ = (T − T_cr )/|T_cr |^[66] ）

Figure 3. Scaling analysis of low-temperature resistance for CeRhGe₃ at pressures near p_c ≈ 21.5 GPa: (a) pressure dependence of the isothermal resistance R^* (R^* = R−R₀ ) at selected temperature range of 2 K≤T≤10 K (The red squares indicate the pressure p_vc and the temperatures at which R* drops by 50% from its value at the critical pressure p_c, and the red line represents the relation between p_vc and temperature, and it’s extrapolation of the square data to 0 K gives the critical end point pressure of the phase transition of the first-order valence state p_cr.); (b) normalized resistance R_nor (R_nor = [R^*−R^*(p_vc)]/R^*(p_vc)) as a function of pressure, the red squares are equivalent to those presented in Fig.3(a); (c) temperature dependence of the R_nor slope $\,\chi$ ($\,\chi$ = |dR_nor/dp$|_{p_{\rm{vc}}} $) at p_vc, the red dashed line represents a Curie-Weiss fit, yielding T_cr = −20 K; (d) collapse of normalized R_nor data as a function of the generalized distance h/$\theta $ from the critical end point, where h = (p− p_vc)/p_vc and $\theta $ = (T − T_cr )/|T_cr|^[66]

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图 4 最佳掺杂的Bi₂Sr₂CaCu₂O_8+δ在不同压力下的R_ab、R_c和交流磁化率Δ$\,\chi $'随温度的变化：(a)～(d)为6.0、7.5、8.2和9.0 GPa下归一化后的R_ab和R_c随温度变化曲线，(e)～(h)为0.8、2.9、5.5、10.3 GPa下归一化电阻（R/R_{120 K}）和交流磁化率随温度变化曲线^[93]

Figure 4. R_ab, R_c and Δ$\,\chi $' as a function of temperature for optimally doped Bi₂Sr₂CaCu₂O_8+δ: normalized R_ab(T) and R_c(T) measured at pressures of 6.0 GPa (a), 7.5 GPa (b), 8.2 GPa (c) and 9.0 GPa (d); Δ$\,\chi $' and R/R_{120 K} at pressures of 0.8 GPa (e), 2.9 GPa (f), 5.5 GPa (g) and 10.3 GPa (h)^[93]

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图 5 最佳掺杂的Bi₂Sr₂CaCu₂O_8+δ中压力导致的2D-3D超导态跃变的温度-压力相图^[93]

Figure 5. Pressure-T_c phase diagram of optimally doped Bi₂Sr₂CaCu₂O_8+δ^[93]

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图 6 Bi₂Sr₂CaCu₂O_8+δ超导体的普适温度-压力相图（右侧是欠掺杂、最佳掺杂和过掺杂Bi₂Sr₂CaCu₂O_8+δ超导体的温度-压力相图^[94]）

Figure 6. Pressure -T_c phase diagrams for Bi₂Sr₂CaCu₂O_8+δ superconductors (Right panels are the phase diagrams established by the experimental results from the under-doped (UD), optimally-doped (OP) and over-doped (OD) samples^[94].)

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图 7 不同磁场下Ca_0.73La_0.27FeAs₂的压力-温度相图^[108]

Figure 7. Temperature-pressure phase diagrams obtained at different magnetic fields for Ca_0.73La_0.27FeAs₂ single crystals^[108]

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图 8 Tl_0.6Rb_0.4Fe_1.67Se₂、K_0.8Fe_1.70Se₂和K_0.8Fe_1.78Se₂的压力- T_c相图^[132]

Figure 8. Pressure-T_c phase diagram for Tl_0.6Rb_0.4Fe_1.67Se₂, K_0.8Fe_1.70Se₂ and K_0.8Fe_1.78Se₂^[132]

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图 9 (a) K_0.8Fe_xSe₂（x=1.70, 1.78）的T_c和采用公式$\,\rho $=$\,\rho $₀+AT^a拟合电阻-温度曲线得到的指数α随压力的演化，(b) K_0.8Fe_1.78Se₂ 在不同压力下的X射线衍射谱（波长0.6888 Å），(c) Fe空位的超晶格峰的峰强随压力的变化^[134]

Figure 9. (a) Pressure dependence of the superconducting transition temperature T_c, and the power α obtained from the fits by relation $\,\rho $=$\,\rho $₀+AT^a for K_0.8Fe_xSe₂ (x=1.70, 1.78) single crystals; (b) X-ray diffraction patterns of K_0.8Fe_1.78Se₂, performed with a wavelength of 0.6888 Å; (c) intensity of the superstructure peak (110) of Fe vacancies as a function of pressure^[134]

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