Characteristic signatures of quantum criticality driven by geometrical frustration

Abstract

Thermodynamic measurements on the Kondo lattice CeRhSn indicate a quantun critical point driven by geometrical frustration.

Uniaxial stress tuning of geometrical frustration in a Kondo lattice

“…Previous low-temperature thermal expansion measurements on CeRhSn with the standard dilatometer, i.e., under very low uniaxial stress of 0.5 MPa, revealed a pronounced anisotropy [18]. While the c-axis expansion coefficient α c /T saturates at low temperatures, indicative of dominating Fermi liquid behavior, the a-axis coefficient α a /T diverges upon cooling (cf.…”

“…In contrast to CePdAl and YbAgGe it remains paramagnetic upon cooling down to at least 50 mK [16,17]. Divergences of the specific heat coefficient, Grüneisen ratio and magnetic Grüneisen parameter indicate that the system is in close vicinity to a zero-field QCP [18]. Particularly striking is the anisotropy of the linear thermal expansion at low temperatures.…”

“…Such behavior is in sharp contrast to quantum criticality in various other Kondo lattices where α/T diverges along all directions [19][20][21][22][23]. The insensitivity of quantum critical entropy to initial stress along the c direction, which leaves geometrical frustration unchanged, indicates a frustration-induced QCP in CeRhSn [18]. This material is thus well suited to investigate whether uniaxial stress can act as novel tuning parameter for quantum criticality in frustrated magnets.…”

“…Since we used a single crystal of rectangular shape with the same cross section at both ends, a uniform stress along the sample is guaranteed which is an important advantage compared to piezo-strain devices. All measurements were performed on a well characterized single crystal studied previously [18]. The applied stress was enhanced by subsequently reducing its cross section.…”

“…Along the a-axis, the previously measured positive α a (T ) > 0 at very small uniaxial pressure of 0.5 MPa indicates an enhancement of Kondo temperature also for a-axis stress. Without a release of geometrical frustration by distortion of the quasi-Kagome lattice [18], a-axis stress therefore cannot induce magnetic order in CeRhSn. In contrast to c-axis uniaxial stress, which leaves geometrical frustration unchanged, a-axis stress, as shown in Fig.…”