We show that the strong Nernst signal observed recently in amorphous superconducting films far above the critical temperature is caused by the fluctuations of the superconducting order parameter. We demonstrate a striking agreement between our theoretical calculations and the experimental data at various temperatures and magnetic fields. Besides, the Nernst effect is interesting not only in the context of superconductivity. We discuss some subtle issues in the theoretical study of thermal phenomena that we have encountered while calculating the Nernst coefficient. In particular, we explain how the Nernst theorem (the third law of thermodynamics) imposes a strict constraint on the magnitude of the Nernst effect.
Nernst Effect and Superconducting Fluctuations in Zn-doped YBa$_{2}$Cu$_{3}$O$_{7-δ}$
报道了用脉冲激光沉积技术生长的Zn掺杂$_{2}$ O $_{3}$外延薄膜的面内电阻率、霍尔效应和能斯特效应的测量结果。的赝能隙温度，$T^*$，确定从电阻率的温度依赖性，不改变与Zn掺杂显着。同时，在$T_{c0}$以上的反常能斯特信号的起始温度（$T^ν$）随着超导转变温度$T_{c0}$的降低而急剧降低，这被解释为类涡旋激发的证据。在混合态下，涡旋能斯特信号的最大值也显著降低，这与Zn杂质导致超流密度降低从而抑制超导电性的假设相一致.给出并讨论了$T^*$、$T^ν$和$T_{c0}$与Zn含量的相图。
A liquid of superconducting vortices generates a transverse thermoelectric response. This Nernst signal has a tail deep in the normal state due to superconducting fluctuations. Here, we present a study of the Nernst effect in two-dimensional hetero-structures of Nb-doped strontium titanate (STO) and in amorphous MoGe. The Nernst signal generated by ephemeral Cooper pairs above the critical temperature has the magnitude expected by theory in STO. On the other hand, the peak amplitude of the vortex Nernst signal below $T_c$ is comparable in both and in numerous other superconductors despite the …
We show that the entropy per quantum vortex per layer in superconductors in external magnetic fields is bounded by the universal value k_B ln 2, which explains puzzling results of recent experiments on the Nernst effect.
We present a complete analysis of the Nernst signal due to superconducting fluctuations in a large variety of superconductors from conventional to unconventional ones. A closed analytical expression of the fluctuation contribution to the Nernst signal is obtained in a large range of temperature and magnetic field. We apply this expression directly to experimental measurements of the Nernst signal in Nb$_x$Si$_{1-x}$ thin films and a URu$_2$Si$_2$ superconductors. Both magnetic field and temperature dependence of the available data are fitted with very good accuracy using only two fitting param…
A Diagrammer's Note on Superconducting Fluctuation Transport for Beginners: II. Hall and Nernst Effects with Perturbational Treatment of Magnetic Field
Colossal thermomagnetic response in the exotic superconductor URu2Si2
当超导体被加热到其临界温度$T_c$以上时，宏观相干性消失，留下热波动的库珀对液滴。$T_c$上的超导涨落效应已经被研究了几十年，它对大多数超导体中的输运、热电和热力学量的影响已经被标准高斯涨落理论很好地理解。横向热电（能斯特）效应是特别敏感的波动，和大能斯特信号中发现的赝能隙制度的低掺杂高$T_c$铜酸盐引起了很多争论，其连接到超导电性的起源。本文报道了在重费米子超导体URu $_2$ Si $_2$中观测到的超导涨落引起的巨大能斯特信号。能斯特系数比超导涨落标准框架内的理论预期值提高了100万倍。这是第一次在任何已知的材料，结果在一个相当大的热磁品质因数接近统一。此外，与传统观点相反，能斯特信号的增强随着杂质散射率的降低而更加显著。这种反常的能斯特效应密切地反映了嵌入在所谓的URu $_2$ Si $_2$的隐序相中的极不寻常的超导态。结果调用可能的手征或贝里相位波动起源于该超导体的拓扑方面，这是与超导序参量的时间反演对称性破缺固有地诱导的有效磁场。
The role of nematic fluctuations for unconventional superconductivity has been subject of intense discussions for many years. In iron-based superconductors, the most established probe for electronic-nematic fluctuations, i.e. the elastoresistivity seems to imply that superconductivity is reinforced by electronic-nematic fluctuations, since the elastoresistivity amplitude peaks at or close to optimal $T_C$. However, on the over-doped side of the superconducting dome, the diminishing elastoresistivity suggests a negligible importance in the mechanism of superconductivity. Here we introduce the N…
We describe an alternating current method to measure the Nernst effect in superconducting thin films at low temperatures. The Nernst effect is an important tool in the understanding superconducting fluctuations and, in particular, vortex motion near critical points. However, in most materials, the Nernst signal in a typical experimental setup rarely exceeds a few $μ$V, in some cases being as low as a few nV. DC measurements of such small signals require extensive signal processing and protection against stray pickups and offsets, limiting the sensitivity of such measurements to $>$5nV. Here we…
Nernst Effect of stripe ordering La$_{1.8-x}$Eu$_{0.2}$Sr$_x$CuO$_4$
我们研究了La $_{1.8-x}$ Eu $_{0.2}$ Sr $_x$ CuO $_4$（$x=0.04$，0.08，0.125，0.15，0.2）的输运性质，特别关注正常态下的能斯特效应.数据中存在各种异常特征。对于$x=0.125$和0.15，在LTT相中电荷条纹有序开始的附近存在扭结状异常，表明条纹有序相中增强的正准粒子能斯特响应。在较高的温度下，除了$x=0.2$的所有掺杂水平表现出进一步的扭结异常的LTO阶段，不能明确地与条纹顺序。此外，在掺杂水平$x=0.125$和$x=0.15$下，条形有序La $_{1.8-x}$ Eu $_{0.2}$ Sr $_x$ CuO $_4$和超导La $_{2-x}$ Sr $_x$ CuO $_4$的能斯特系数之间的直接比较揭示了仅微弱的差异。我们的研究结果对任何解释空穴掺杂铜酸盐能斯特响应的方案提出了很高的要求。
Correlation between incoherent phase fluctuations and disorder in Y$_{1-x}$Pr$_x$Ba$_2$Cu$_3$O$_{7-δ}$ epitaxial films from Nernst effect measurements
本文报道了YPDMATHABMM Pr $_x$ Ba $_2$ Cu $_3$ O $_{7-δ}$（Pr-YBCO，0 $\leq x\leq$ 0.4）外延薄膜在宽温度和磁场范围内的能斯特效应、电阻率和霍尔角的测量结果。虽然霍尔和电阻率的数据表明一个广泛的赝能隙制度，根据早期的结果，这些第一次测量的能斯特效应Pr-YBCO超导转变温度以上的大信号（T $_c$）。这种效应归因于T $_c$上存在的相位非相干凝聚体中的类涡旋激发。对YBCO铜族化合物的无序度和相涨落区宽度之间的关系已经建立，这表明无无序的YBa $_2$ Cu $_3$ O $_{7-δ}$的T $_c\approx$为110 K.
In a liquid of superconducting vortices, a longitudinal thermal gradient generates a transverse electric field. This Nernst signal peaks at an intermediate temperature and magnetic field, presumably where the entropy difference between the vortex core and the superfluid environment is largest. There is a puzzling similarity of the amplitude of this peak across many different superconductors. This peak can be assimilated to a minimum in the viscosity to entropy density ratio of the vortex liquid. Expressed in units of $\frac{\hbar}{k_B}$, this minimum is one order of magnitude larger than what …
The strange-metal state is a crucial problem in condensed matter physics highlighted by its ubiquity in almost all major correlated systems[1-7]. Its understanding could provide important insight into high-Tc superconductivity[2] and quantum criticality[8]. However, with the Fermi liquid theory failing in strange metals, understanding the highly unconventional behaviors has been a long-standing challenge. Fundamental aspects of strange metals remain elusive, including the nature of their charge carriers[1]. Here, we report the observation of a giant Nernst response in the strange-metal state i…
We present the magneto-transport and the thermoelectric (Seebeck and Nernst coefficient) studies of the Nb-doped Bi2Se3 topological superconductor. The angle-dependent magnetoresistance study highlights the anisotropy in the upper critical field (Hc2) with the anisotropy parameter Gamma ~1.2. We observed a gradual decrease in low-temperature Hall resistivity on the application of magnetic field like any conventional superconductor, instead of the finite Hall resistivity which was linked to the chiral superconducting phase. The estimated value of the carrier concentration (~ 10^19 cm-3) for Nb0…
We investigate the spin-Nernst effect in time-reversal invariant topological superconductors, and show that it provides a smoking-gun evidence for helical Cooper pairs. The spin-Nernst effect stems from asymmetric, in spin space, scattering of quasiparticles at nonmagnetic impurities, and generates a transverse spin current by the temperature gradient. Both the sign and the magnitude of the effect sensitively depend on the scattering phase shift at impurity sites. Therefore the spin-Nernst effect is uniquely suitable for identifying time-reversal invariant topological superconducting orders.
