High-field moment polarization in the ferromagnetic superconductor UCoGe

Knafo, William; Matsuda, Tatsuma D.; Aoki, Dai; Hardy, F.; Scheerer, Gernot; Ballon, Géraldine; Nardone, Marc; Zitouni, Abdelkrim; Meingast, C.; Flouquet, J.

doi:10.1103/physrevb.86.184416

Cited by 51 publications

(58 citation statements)

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“…The spontaneous magnetization in the ferromagnetic (FM) state is very small, M 0 ≈ 0.05 µ B /U with Ising moments along the c axis [25] and under magnetic field the magnetization is strongly anisotropic with M c > M b > M a . For H c, M c increases non-linearly with field and shows a broad kink at H ≈ 23 T, but even at H ∼ 50 T, with M c ≈ 0.65 µ B /U at T = 1.5 K, it is far from saturation [26]. Another striking point is the detection of well separated anomalies in the magnetoresistance for H c [27][28][29] far above the collapse of the FM fluctuations (H > 1 T) [30] while M (H) rules out thermodynamic phase transitions under magnetic field at least down to 1.5 K [26].…”

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confidence: 95%

“…The magnetization up to 50 T [26] has a strongly non-linear field dependence suggesting that the electronic magnetic response must vary strongly with the magnetic field while the FM fluctuations are already fully suppressed for H > 1 T along the c axis [24,30]. Thus the electronic instabilities seem to occur in the paramagnetic regime without any additional phase transitions and far above the field where the FM intersite magnetic correlations collapse.…”

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Lifshitz Transitions in the Ferromagnetic Superconductor UCoGe

et al. 2016

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We present high field magnetoresistance, Hall effect and thermopower measurements in the Isingtype ferromagnetic superconductor UCoGe. Magnetic field is applied along the easy magnetization c axis of the orthorhombic crystal. In the different experimental probes we observed five successive anomalies at H ≈ 4, 9, 12, 16, and 21 T. Magnetic quantum oscillations were detected both in resistivity and thermoelectric power. At most of the anomalies, significant changes of the oscillation frequencies and the effective masses have been observed indicating successive Fermi surface instabilities induced by the strong magnetic polarization under magnetic field.PACS numbers: 71.27.+a, 71.18.+y, 74.70.Tx Lifshitz transitions (LTs) are continuous quantum phase transitions at zero temperature where the topology of the Fermi surface (FS) changes due to the variation of the Fermi energy and the band structure of a metal [1,2]. They have been already studied in the sixties and can be induced by chemical doping, pressure, or strong magnetic field (H). However, only recently LTs have been proposed as the driving force to modify the ground-state properties in strongly correlated electron systems. The interplay of a LT with magnetic quantum phase transitions in heavy fermion systems has been treated in various theoretical models (see e.g. Refs. 3-8). The influence of LTs on the appearance of superconductivity is discussed in cuprates [9,10], iron pnictides [11,12] Usually the electronic band structure is a rather robust property of the metallic state, especially when applying magnetic fields. Only when the magnetic ground state is modified, changes of the FS may be detected. In a normal metal the Zeeman splitting induced by accessible magnetic fields is weak with respect to the Fermi energy which is usually of the order of a few eV. Importantly, in heavy fermion compounds the Fermi energy scale is significantly reduced due to the hybridization of the conduction and the localized f electrons. Thus, the Zeeman splitting of the flat bands crossing the Fermi level can be so strong that one of the spin-split FS sheets is continuously suppressed and undergoes a LT. In heavyfermion systems a LT is often associated to a change in the intersite and/or local magnetic fluctuations, see e.g. In this Letter we report on FS properties of UCoGe under magnetic field, which orders ferromagnetically at T C = 2.7 K. Remarkably, homogeneous coexistence of ferromagnetism and heavy-fermion superconductivity is observed below T sc = 0.6 K [23]. UCoGe crystallizes in an orthorhombic structure (space group P nma). In order to study the field dependence of the FS properties in a highly polarizable heavy fermion system with small FS pockets we performed systematic resistivity (ρ), Hall effect (ρ xy ) and thermopower (S) experiments in UCoGe. Two different samples (labelled S1 and S2) with residual resistivity ratios [RRR = ρ(300 K)/ρ(1 K)] of 105 and 36 have been prepared for experiments with electrical or heat current along the b and a axis respectively.

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Lifshitz Transitions in the Ferromagnetic Superconductor UCoGe

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“…1,7 Spontaneous moment appears parallel to the c-axis and its magnetization curve exhibits meta-magnetism when magnetic field H is applied to one of the hard axes (b axis) with a notable mass enhancement. 8 This meta-magnetism is particularly prominent in URhGe and the moment gradually tilts with field and finally aligns parallel to H at 12 T.…”

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p-wave superconductivity near a transverse saturation field

Hattori

Tsunetsugu

2013

Phys. Rev. B

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We investigate reentrant superconductivity in an Ising ferromagnetic superconductor URhGe under a transverse magnetic field hx. The superconducting transition temperature for p-wave order parameters Tsc is calculated and shows two domes as a function of hx. We find strong enhancement of Tsc in the high-field dome near a saturation field hs where the spins align in the transverse direction. Soft magnons generate strong attractive interactions there. Spin components of the pairing show a significant change between hxhs. We also discuss the appearance of superconductivity with zero-spin pair due to cancellation between external and exchange fields.PACS numbers: 74.20.Mn, Ferromagnetic superconductivity (SC) has attracted much attention in condensed matter physics in the last decade.1 U-based heavy-fermion compounds such as UGe 2 , URhGe, UIr, and UCoGe show unconventional SC within their ferromagnetic phases.2-5 Non-unitary SC's 6 are believed to appear in these compounds and both the SC and ferromagnetism are caused in the f electrons at U sites. Their pairing mechanism and symmetry as well as novel self-induced vortex states are central issues to be clarified in the modern theory of unconventional superconductors. Two isomorphic compounds, UTGe(T=Rh, Co), exhibit SC at ambient pressure within their ferromagnetic state and have a similar Ising type anisotropy of magnetization.1,7 Spontaneous moment appears parallel to the c-axis and its magnetization curve exhibits meta-magnetism when magnetic field H is applied to one of the hard axes (b axis) with a notable mass enhancement.8 This meta-magnetism is particularly prominent in URhGe and the moment gradually tilts with field and finally aligns parallel to H at 12 T. 9Superconductivity appears below the transition temperature T sc =0.24 K for H=0, and T sc decreases with H and disappears at 2 T for H b.9 Interestingly, SC reappears above 8 T and shows the highest T sc =0.42 K at 12 T. 9Theories of ferromagnetic SC have been developed by various groups, 10-15 especially for UGe 2 . [16][17][18][19] In this paper, we focus on the reentrant SC in URhGe, which has not been investigated theoretically. The physics of the reentrant SC is quite different from that in UGe 2 . 16-18The point is the presence of soft magnons in the Ising systems with transverse fields. We clarify it by extending the Scharnberg-Klemm (SK) theory 20 in the presence of ferromagnetism and transverse magnetic fields. In particular, we demonstrate (i) strong enhancement of T sc near the saturation field, and (ii) strong field dependence in spin components (d-vector) of p-wave pairing.We consider a system of conduction electrons as shown in Fig. 1, coupled to ferromagnetic localized spins, which have a magnetization M in the z-direction (corresponding to the c axis in URhGe at H=0). We apply a transverse magnetic field H x along the b axis and study its ef- fects on ferromagnetic SC. For conduction electrons, we use isotropic dispersion ε p =p 2 /2m * , ignoring complex band structures. 21 ...

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“…The two slopes are related to AHE which dominates the change at fields below the kink field B k and OHE which dominates the change at fields above the kink field. Below the kink field, B ≤ B k , Hall resistance increases with the field, due to the variation of the magnetization (increasing with field) [12,13], producing the large anomalous Hall effect. Near B k there is rounding of R Hall (B) above which (B > B k ) the field dependence of the negative, ordinary Hall effect survives (the slope of R Hall (B) decreases with increasing field).…”

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confidence: 99%

“…Consequently, the kink field B k is the moment polarization field in UCoGe and the induced moment polarization is driven to higher B k with the rotation from the c axis. Recently, systematic magnetization and magnetoresistance measurements in UCoGe in high magnetic fields have shown that at low temperature a moment polarization in UCoGe in a field c B of 23 T and b B of 50 T leads to well defined anomalies in both magnetization and magnetoresistance [13] as also are observed here in magnetoresistance and Hall effect in fields up to 18 T. All present studies show that the kink anomaly is a common feature in UCoGe since it is also present in the magnetoresistance and thermopower for .…”

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confidence: 99%

HALL EFFECT STUDIES OF THE SUPERCONDUCTING FERROMAGNET UCoGe

Krstovska

Steven²,

Kiswandhi³

et al. 2017

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We find that the Hall effect in a single crystal of UCoGe varies as a function of the angle  between the applied magnetic field and the easy magnetic axis up to fields of 18 T at 0.2 K, i.e. in the region where both superconductivity and ferromagnetic order coexist. Instead of following the conventional cos dependence the two components that comprise the total Hall resistance, the anomalous and ordinary Hall effect, exhibit quite an unusual behavior with the field direction. The anomalous Hall effect is found to be determined by the parallel component of the magnetization. We suggest that the field induced changes in magnetization due to the field rotation play an important role in the observed unusual behavior. The ordinary Hall effect cannot be described by the simple relation to the perpendicular component of the magnetic field implying that this component of the Hall effect may be also affected by the variations in magnetization at the characteristic field (kink field). A field induced moment polarization is also observed in Hall effect as in magnetoresistance, which advances previous findings in UCoGe. The Hall effect slope reverses sign at the kink field indicative of small but possible Fermi surface reconstruction around this field. Our findings show that in UCoGe multiple mechanisms contribute to the observed field induced moment polarization at the kink field.

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High-field moment polarization in the ferromagnetic superconductor UCoGe

Cited by 51 publications

References 24 publications

Lifshitz Transitions in the Ferromagnetic Superconductor UCoGe

Lifshitz Transitions in the Ferromagnetic Superconductor UCoGe

p-wave superconductivity near a transverse saturation field

HALL EFFECT STUDIES OF THE SUPERCONDUCTING FERROMAGNET UCoGe

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