Criticalities in the itinerant ferromagnetUGe2

Abstract

We provide a microscopic description of the magnetic properties of UGe2 and in particular, of its both classical and quantum critical behavior. Namely, we account for all the critical points: the critical ending point (CEP) at the metamagnetic phase transition, the tricritical point, and the quantum critical end point at the ferromagnetic to paramagnetic phase transition. Their position agrees quantitatively with experiment. Additionally, we predict that the metamagnetic CEP can be traced down to zero temperature and becomes quantum critical point by a small decrease of both the total electron concentration and the external pressure. The system properties are then determined by the quantum critical fluctuations appearing near the instability point of the Fermi surface topology.Introduction. Attempts to determine the quantum critical behavior and the corresponding critical points (QCPs) have attracted much attention due to the unique phenomena with singular physical properties associated with them as temperature T → 0 and other parameters (pressure p, applied field H, or electron concentration n) are varied [1][2][3]. Additionally, in the canonical case-the heavy fermion systems-unconventional superconductivity often appears near those QCPs making the quantum critical fluctuations the primary pairing inducing factor. Also, the classical critical points (CCPs) and their evolution towards QCP provide the testing ground for study of detailed quantitative behavior of different systems [4,5].

Tricritical wings in UGe2: A microscopic interpretation

“…A similar idea concerning the emergence of two distinct FM phases in UGe 2 was also obtained earlier within the phenomenological picture based on the Stoner theory incorporating a two-peak structure of the density of states in a single band [25]. In brief, our microscopic model extended to the case of T > 0 [14] describes well emergence of all CPs on the magnetic phase diagram of UGe 2 [8][9][10] in the semiquantitative manner [14]. Here we compare in detail our results with the experimental data, namely predicted second order transition line joining the TCP with the corresponding QCEP.…”

“…One of the first approaches, based on the single-band model describing tricritical wings, was the work by Belitz, et al [11]. However, the microscopic description of the magnetic phase diagram with all the CPs including also CEP at the metamagnetic transition, as observed in UGe 2 , has been missing until our recent works [13,14].…”

“…One of the first approaches, based on the single-band model describing tricritical wings, was the work by Belitz, et al [11]. However, the microscopic description of the magnetic phase diagram with all the CPs including also CEP at the metamagnetic transition, as observed in UGe 2 , has been missing until our recent works [13,14].Our analysis is based on the (two-orbital) Anderson * marcin.abram@uj.edu.pl † marcin.wysokinski@uj.edu.pl ‡ ufspalek@if.uj.edu.pl lattice model (ALM) [13,14], often referred to as the periodic Anderson model. Findings for UGe 2 , both from first principle calculations and experiments are: the quasitwo-dimensional character of the Fermi surface [15], a uniaxial anisotropy for magnetization [16], U-U interatomic distance above the so-called Hill limit [1], and the paramagnetic moment per U atom different from that expected for either f 3 or f 2 atomic configurations [2,17].…”

“…The influence of factor (i) has the following importance. For exemplary filling n = 1.6 we have shown [14] that the relative position of the TCP and CEP (cf. Fig.1) is the same as that seen in the experiments [9,10].…”

“…Our analysis is based on the (two-orbital) Anderson * marcin.abram@uj.edu.pl † marcin.wysokinski@uj.edu.pl ‡ ufspalek@if.uj.edu.pl lattice model (ALM) [13,14], often referred to as the periodic Anderson model. Findings for UGe 2 , both from first principle calculations and experiments are: the quasitwo-dimensional character of the Fermi surface [15], a uniaxial anisotropy for magnetization [16], U-U interatomic distance above the so-called Hill limit [1], and the paramagnetic moment per U atom different from that expected for either f 3 or f 2 atomic configurations [2,17].…”