A mechanism for the strange metal phase in rare-earth intermetallic compounds

Abstract

Significance The elusive strange metal phase (ground state) was observed in a variety of quantum materials, notably in f -electron–based rare-earth intermetallic compounds. Its emergence has remained unclear. Here, we propose a generic mechanism for this phenomenon driven by the interplay of the gapless fermionic short-ranged antiferromagnetic spin correlation and critical bosonic charge fluctuations near a Kondo breakdown quantum phase transition. It is manifested as a fluctuating Kondo-scattering–stabilized critical (gapless) fermionic spin liquid. It shows ω / T scaling in dynamical electron scattering rate, a signature of quantum criticality. Our results on quasilinear-in-temperature scattering rate and logarithmic-in-temperature divergence in specific heat coefficient as temperature vanishes were recently seen in CePd 1 − x Ni x Al.

Is the optical conductivity of heavy fermion strange metals Planckian?

“…Forcing (extended) Drude forms to the data bears the risk to overlook the essential physics. Strange metals may be governed by exotic excitations or even the absence of any well-defined quasiparticles (Si et al, 2001;Coleman et al, 2001;Senthil et al, 2004;Phillips, 2011;Chang et al, 2018;Patel and Sachdev, 2018;Komijani and Coleman, 2019;Banerjee et al, 2021;Cai et al, 2020;Cha et al, 2020;Guo et al, 2020;Balm et al, 2020;Lee, 2021;Else and Senthil, 2021;Wang et al, 2022;Caprara et al, 2022), so they defy description by the above models and require alternative approaches.…”

Is the optical conductivity of heavy fermion strange metals Planckian?

“…Forcing (extended) Drude forms to the data bears the risk to overlook the essential physics. Strange metals may be governed by exotic excitations or even the absence of any welldefined quasiparticles (Coleman et al, 2001;Si et al, 2001;Senthil et al, 2004;Phillips, 2011;Chang et al, 2018;Patel and Sachdev, 2018;Komijani and Coleman, 2019;Balm et al, 2020;Cai et al, 2020;Cha et al, 2020;Guo et al, 2020;Banerjee et al, 2021;Else and Senthil, 2021;Lee, 2021;Caprara et al, 2022;Wang et al, 2022), so they defy description by the above models and require alternative approaches.…”

Nonlocal Kondo effect and two-fluid picture revealed in an exactly solvable model

“…Underlying the rich emergent quantum phenomena of heavy fermion systems 1,2 is the local-to-itinerant transition of f -electrons controlled by the interplay of Kondo and Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions [3][4][5][6][7][8][9][10][11][12][13][14][15] . Below the so-called coherence temperature T * , a large amount of experimental observations have pointed to the coexistence of local and itinerant characters of f -electrons as captured phenomenologically by the two-fluid model [16][17][18][19][20][21][22] , which assumes the coexistence of an itinerant heavy electron fluid formed by hybridized (screened) f -moments and a (classical) spin liquid of residual unhybridized f -moments.…”

“…While it seems to be supported experimentally by the Hall coefficient jump under magnetic field extrapolated to zero temperature in YbRh 2 Si 2 27 and the de Haas-van Alphen experiment under pressure in CeRhIn 5 28 , it was lately challenged by a number of angle-resolved photoemission spectroscopy measurements showing signatures of large Fermi surfaces 29 or band hybridization above the magnetically ordered state 30 . In theory, the Kondodestruction scenario could be derived under certain local or mean-field approximations, such as the dynamical large-N approaches assuming independent electron baths coupled to individual impurity 9,10,14 and the extended dynamical mean-field theory by mapping the Kondo lattice to a single impurity Bose-Fermi Kondo model 4 . Since the corresponding spin-1 2 single-or two-impurity problems only allow for two stable fixed points in the strongcoupling limit and the decoupling limit [31][32][33] , these approaches unavoidably predicted a single QCP associated with Kondo destruction.…”