Approaching quantum criticality in a partially geometrically frustrated heavy-fermion metal

Fritsch, V.; Bagrets, N.; Goll, G.; Kittler, W.; Wolf, Michael; Grube, K.; Huang, C. L.; Löhneysen, H. v.

doi:10.1103/physrevb.89.054416

Cited by 67 publications

(57 citation statements)

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“…At any field-tunable QCP, Γ mag displays a universal divergence and sign change upon tuning the field across the critical field [35,36]. Our thermodynamic investigation of CePd 1−x Ni x Al reveals 2D field-induced quantum criticality for x = 0.05 and x = 0.1 and a (zero-field) concentration tuned QCP at x c ≈ 0.15 in accordance with previous results on polycrystals [25]. Most interestingly, we find a positive contribution in Γ mag (B) near 2.5 T, in addition to quantum critical behavior, indicative of a field-induced suppression of magnetic entropy.…”

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“…In CePdAl the magnetic frustration gives rise to unusual magnetic ordering [21][22][23][24]. It has been shown previously using polycrystals that the material can be tuned through a QCP with the aid of chemical pressure, realized by partial substitution of Pd by Ni [25].CePdAl exhibits a strong magnetic anisotropy with the susceptibility ratio χ c /χ ab ≈ 15 at T = 5 K, which is attributed to crystalline-electric-field and exchange anisotropies [26]. Upon cooling, the electrical resistivity exhibits a − ln T dependence from 20 to 6 K, followed by a coherence maximum at 4 K and a subsequent decrease [27,28].…”

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Signature of frustrated moments in quantum critical CePd1−xNixAl

et al. 2016

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CePdAl with Ce 4f moments forming a distorted kagomé network is one of the scarce materials exhibiting Kondo physics and magnetic frustration simultaneously. As a result, antiferromagnetic (AF) order setting in at TN = 2.7 K encompasses only two thirds of the Ce moments. We report measurements of the specific heat, C, and the magnetic Grüneisen parameter, Γmag, on single crystals of CePd1−xNixAl with x ≤ 0.16 at temperatures down to 0.05 K and magnetic fields B up to 8 T. Field-induced quantum criticality for various concentrations is observed with the critical field decreasing to zero at xc ≈ 0.15. Remarkably, two-dimensional (2D) AF quantum criticality of Hertz-Millis-Moriya type arises for x = 0.05 and x = 0.1 at the suppression of 3D magnetic order. Furthermore, Γmag(B) shows an additional contribution near 2.5 T for all concentrations which is ascribed to correlations of the frustrated one third of Ce moments.New quantum states of matter, arising in materials with competing interactions and multiple energetically degenerate configurations are of strong interest in condensed matter physics. For example, unconventional superconductivity is found near quantum critical points (QCPs) [1][2][3][4][5] and spin-liquid phases, driven by strong frustration have been realized in magnetic insulators [6,7]. However, there are only few studies on metallic frustrated magnets [8], and the effect of frustration on quantum criticality in metals has rarely been investigated experimentally. Rare-earth heavy-fermion (HF) metals, consisting of 4f moments coupled to conduction electrons by an exchange interaction J, are ideally suited for this purpose. Since J governs the competition between the indirect Ruderman-Kittel-KasuyaYosida (RKKY) exchange and the Kondo interaction [9], QCPs can be realized by variation of J with pressure, chemical composition or magnetic field [10][11][12]. Unconventional quantum criticality with a Kondo breakdown and a spin-liquid phase of localized 4f moments being decoupled from conduction electrons has been predicted for high degree of frustration [13]. The 'global phase diagram', which classifies the electronic and magnetic ground states for HF systems, treats J and the strength of quantum fluctuations arising from frustration as two independent parameters [14-16].The effect of geometrical frustration in Kondo lattices has been recognized in hexagonal systems crystallizing in the ZrNiAl structure. Here, the 4f electrons form a structure of equilateral corner-sharing triangles in the ab plane, which can be described as a distorted kagomé network. For YbAgGe, the geometrical frustration leads to a series of almost degenerate magnetic states tuned by magnetic fields and novel quantum bicritical behavior [17][18][19]. CeRhSn does not display long-range order and is located close to a QCP driven by geometrical frustration [20]. In CePdAl the magnetic frustration gives rise to unusual magnetic ordering [21][22][23][24]. It has been shown previously using polycrystals that the material can be tuned throug...

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Signature of frustrated moments in quantum critical CePd1−xNixAl

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“…While most of previous studies of KHLM focused on the square lattice, the two-dimensional lattice with geometrical frustration provides additional tuning factor into the phase transitions in HF systems, such as CePd 1−x Ni x Al [16] on Kagome lattice, and YbAgGe [17,18], YbAl 3 C 3 [19,20] on triangular lattices. For Yb 2 Pt 2 Pb [21,22], a KHLM on Shastry-Sutherland square lattice (SSL) [23] was proposed, in which the diagonal Heisenberg exchanges J 2 provide geometrical frustration, and the phase diagram was determined on J k -J 2 plane within mean-field approximation [24,25].…”

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Phase diagram of the Kondo-Heisenberg model on honeycomb lattice with geometrical frustration

Song

Liu

2016

EPL

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We calculated the phase diagram of the Kondo-Heisenberg model on two-dimensional honeycomb lattice with both nearest-neighbor and next-nearest-neighbor antiferromagnetic spin exchanges, to investigate the interplay between RKKY and Kondo interactions at presence of magnetic frustration. Within a mean-field decoupling technology in slave-fermion representation, we derived the zero-temperature phase diagram as a function of Kondo coupling J k and frustration strength Q. The geometrical frustration can destroy the magnetic order, driving the original antiferromagnetic (AF) phase to non-magnetic valence bond state (VBS). In addition, we found two distinct VBS. As J k is increased, a phase transition from AF to Kondo paramagnetic (KP) phase occurs, without the intermediate phase coexisting AF order with Kondo screening found in square lattice systems. In the KP phase, the enhancement of frustration weakens the Kondo screening effect, resulting in a phase transition from KP to VBS. We also found a process to recover the AF order from VBS by increasing J k in a wide range of frustration strength. Our work may provide deeper understanding for the phase transitions in heavy-fermion materials, particularly for those exhibiting triangular frustration.

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“…Magnetic frustration adds complexity to this scenario [9,10] by introducing quantum fluctuations that favor local-moment singlet formation over magnetic order [11]. Several unconventional phases result from this competition, including a metallic valence bond solid (VBS) in YbAl 3 C 3 [12], partial magnetic order in CePd 1−x Ni x Al [13,14], and quantum criticality without tuning in CeRhSn [15]. Other proposed possibilities, such as fractionalized quantum spin liquids (QSLs) [16], remain experimentally elusive.…”

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Filling-enforced nonsymmorphic Kondo semimetals in two dimensions

et al. 2017

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We study the competition between Kondo screening and frustrated magnetism on the nonsymmorphic Shastry-Sutherland Kondo lattice at a filling of two conduction electrons per unit cell. A previous analysis of this model identified a set of gapless partially Kondo screened phases intermediate between the Kondo-destroyed paramagnet and the heavy Fermi liquid. Based on crystal symmetries, we argue that (i) both the paramagnet and the heavy Fermi liquid are semimetals protected by a glide symmetry; and (ii) partial Kondo screening breaks the symmetry, removing this protection and allowing the partially-Kondo-screened phase to be deformed into a Kondo insulator via a Lifshitz transition. We confirm these results using large-N mean field theory and then use non-perturbative arguments to derive a generalized Luttinger sum rule constraining the phase structure of 2D non-symmorphic Kondo lattices beyond the mean-field limit.Introduction.-The interplay between the Kondo effect and magnetism in heavy fermion materials is a paradigmatic setting for competing electronic order [1]. In these rare-earth intermetallic compounds a lattice of local moments from strongly correlated d or f orbitals can hybridize with itinerant conduction electrons to form a heavy Fermi liquid (FL), with a 'large' Fermi surface that incorporates both constituents. Intermoment exchange induced by the Ruderman-Kittel-Kasuya-Yosida (RKKY) mechanism can suppress Kondo screening in favor of magnetic order, and much theoretical and experimental effort has focused on studying the intervening quantum critical point [2][3][4][5][6][7][8]. Magnetic frustration adds complexity to this scenario [9,10] by introducing quantum fluctuations that favor local-moment singlet formation over magnetic order [11]. Several unconventional phases result from this competition, including a metallic valence bond solid (VBS) in YbAl 3 C 3 [12], partial magnetic order in CePd 1−x Ni x Al [13,14], and quantum criticality without tuning in CeRhSn [15]. Other proposed possibilities, such as fractionalized quantum spin liquids (QSLs) [16], remain experimentally elusive.

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Approaching quantum criticality in a partially geometrically frustrated heavy-fermion metal

Cited by 67 publications

References 50 publications

Signature of frustrated moments in quantum critical CePd1−xNixAl

Signature of frustrated moments in quantum critical CePd1−xNixAl

Phase diagram of the Kondo-Heisenberg model on honeycomb lattice with geometrical frustration

Filling-enforced nonsymmorphic Kondo semimetals in two dimensions

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