Nematic state in CeAuSb$_{2}$

面内场作用下Sr $_3$ Ru $_2$ O $_7$向列性和量子临界性的压力研究

Pressure study of nematicity and quantum criticality in Sr$_3$Ru$_2$O$_7$ for an in-plane field

研究了Sr $_3$ Ru $_2$ O $_7$的相变与量子临界性的关系。在环境压力下，当施加的磁场靠近\textit{c}轴时，一个双相与变磁量子临界终点（QCEP）相关联。然而，我们发现，这种变磁性转变不产生相同的磁共振签名时，QCEP达到流体静压与施加在\textit{ab}平面的字段。此外，在接近但不正好处于第二变磁性异常的\textit{ab}平面中施加的场所看到的第二变磁性相持续存在，对最高施加压力16.55千巴的变化最小。总之，我们的研究结果表明，变磁量子临界可能不是必要的Sr $_3$ Ru $_2$ O $_7$中的α相的形成。

Elastic properties of hidden order in URu$_{\text2}$Si$_{\text2}$ are reproduced by a staggered nematic

We develop a phenomenological mean field theory describing the hidden order phase in URu$_{\text2}$Si$_{\text2}$ as a nematic of the $\text B_{\text{1g}}$ representation staggered along the $c$-axis. Several experimental features are reproduced by this theory: the topology of the temperature--pressure phase diagram, the response of the elastic modulus $(C_{11}-C_{12})/2$ above the transition at ambient pressure, and orthorhombic symmetry breaking in the high-pressure antiferromagnetic phase. In this scenario, hidden order is characterized by broken rotational symmetry that is modulated along t…

Highly Anisotropic Superconducting Gap in Nematically Ordered and Tetragonal Phases of FeSe$_{1-x}$S$_x$

FeSe has a unique ground state in which superconductivity coexists with a nematic order without long-range magnetic ordering at ambient pressure. Here, to study how the pairing interaction evolves with nematicity, we measured the thermal conductivity and specific heat of FeSe$_{1-x}$S$_x$, where the nematicity is suppressed by isoelectronic sulfur substitution. We find that in the whole nematic ($0\leq x \leq 0.17$) and tetragonal ($x=0.20$) regimes, the application of small magnetic field causes a steep increase of both quantities. This indicates the existence of deep minima or line nodes in …

Decoupled nematic and magnetic criticality in FeSe$_{1-x}$S$_{x}$

Electronic nematicity in correlated metals often occurs alongside another instability such as magnetism. As a result, the question remains whether nematicity alone can drive unconventional superconductivity or anomalous (quantum critical) transport in such systems. In FeSe, nematicity emerges in isolation, providing a unique opportunity to address this question. Studies to date, however, have proved inconclusive; while signatures of nematic criticality are observed upon sulfur substitution, they appear to be quenched under the application of pressure due to the emergent magnetism. Here, we stu…

Electron-Electron Interactions and the Paired-to-Nematic Quantum Phase Transition in the Second Landau Level

In spite of its ubiquity in strongly correlated systems, the competition of paired and nematic ground states remains poorly understood. Recently such a competition was reported in the two-dimensional electron gas at filling factor $ν=5/2$. At this filling factor a pressure-induced quantum phase transition was observed from the paired fractional quantum Hall state to the quantum Hall nematic. Here we show that the pressure induced paired-to-nematic transition also develops at $ν=7/2$, demonstrating therefore this transition in both spin branches of the second orbital Landau level. However, we f…

Magnetic field-induced softening of spin waves and hard-axis order in Kondo-lattice ferromagnet CeAgSb$_{2}$

A significant number of Kondo-lattice ferromagnets order perpendicular to the easy magnetization axis dictated by the crystalline electric field. The nature of this phenomenon has attracted considerable attention, but remains poorly understood. In the present paper we use inelastic neutron scattering supported by magnetization and specific heat measurements to study the spin dynamics in the hard-axis ferromagnet CeAgSb2. In the zero field state we observed two sharp magnon modes, which are associated with Ce ordering and extended up to $\approx 3 meV with a considerable spin gap of 0.6 meV. Ap…