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Heavy Fermion Superconductivity: 5f vs 4f
Zachary Fisk,Yoshinori Haga 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.3
Heavy electron materials are the only class of materials in which we know where to look forsuperconductivity. We discuss the relation between single ion and dense Kondo heavy electronphysics, what sets the energy scale in these materials, the ways in which their low temperatureexotic superconductivity is a prototype for all highly correlated electron superconductivity and thesimilarities between the 4f and 5f heavy Fermion materials.
Adham Amyan,Pintu Das,Jens M¨uller,Zachary Fisk 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.10
We report measurements of weakly nonlinear electronic transport, as measured by third-harmonic voltage generation V3ω, in the low-carrier density semimetallic ferromagnet EuB6, which exhibits an unusual magnetic ordering with two consecutive transitions at Tc1 = 15.6K and Tc2 = 12.5K. In contrast to the linear resistivity, the third-harmonic voltage is sensitive to the microgeometry of the electronic system. Our measurements provide evidence for magnetically-driven electronic phase separation consistent with the picture of percolation of magnetic polarons (MP), which form highly conducting magnetically ordered clusters in a paramagnetic and less conducting background. Upon cooling in zero magnetic field through the ferromagnetic transition, the dramatic drop in the linear resistivity at the upper transition Tc1 coincides with the onset of nonlinearity, and upon further cooling is followed by a pronounced peak in V3ω at the lower transition Tc2 . Likewise, in the paramagnetic regime, a drop of the material’s magnetoresistance R(H) precedes a magnetic-fieldinduced peak in nonlinear transport. A striking observation is a linear temperature dependence of V peak 3ω (H). We suggest a picture where at the upper transition Tc1 the coalescing MP form a conducting path giving rise to a strong decrease in the resistance. The MP formation sets in at around T∗ ∼ 35K below which these entities are isolated and strongly fluctuating, while growing in number. The MP then start to form links at Tc1 , where percolative electronic transport is observed. The MP merge and start forming a continuum at the threshold Tc2 . In the paramagnetic temperature regime Tc1 < T < T∗, MP percolation is induced by a magnetic field, and the threshold accompanied by charge carrier delocalization occurs at a single critical magnetization.
Naoyuki Tateiwa,Yoshinori Haga,Tatsuma D. Matsuda,Etsuji Yamamoto,Yoshichika Onuki,Zachary Fisk 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.3
We have studied the high-pressure magnetic property in UGe2 where ferromagnetic superconductivityappears under high pressure. In this study, we focus on the magnetic property at pressuresabove the ferromagnetic critical pressure Pc =1.6 GPa. The temperature and magnetic field dependencesof the dc-magnetization have been measured under high pressures up to 5.1 GPa by using aceramic anvil high pressure cell. At pressures above Pc, the magnetic susceptibility χ shows a broadmaximum around Tχmax and the magnetization at 2.0 K shows an abrupt increase (metamagnetictransition) at Hc. With increasing pressure, the peak structure in χ becomes broader, and thepeak position Tχmax moves to the higher temperature region. The metamagnetic field Hc increasesrapidly with increasing pressure. At pressures above 4.1 GPa, χ shows a simple temperature dependence,and the magnetization increases linearly with increasing field. These phenomena in UGe2resemble to those in the intermetallic compounds of 3d transition metals such as Co(S1−xSex) andYCo2. We discuss the experimental results by using the phenomenological spin-fluctuation theory.
Single Crystal Growth and Physical Properties of UT2Al20 (T=Transition Metal)
Yuji Matsumoto,Tatsuma D. Matsuda,Naoyuki Tateiwa,Etsuji Yamamoto,Yoshinori Haga,Zachary Fisk 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.3
We have studied the single crystal growth and the physical properties of the UT2Al20 system. Wehave successfully grown UT2Al20 (T = Cr, Ti, W and Mo) using Al self flux and have characterizedthe crystals using electron probe microanalyzer (EPAM) and X-ray diffractometer. We have alsomeasured their magnetic and electric properties. The ground states of UT2Al20 (T = Cr, Mo andW ) are Pauli paramagnetic as is likely also in UTi2Al20. The effective masses of UCr2Al20 andUTi2Al20 are only weakly enhanced.
Magnetic Phase Diagram of UCoAl
Tatsuma D. Matsuda,Naoyuki Tateiwa,Etsuji Yamamoto,Yoshinori Haga,Yoshichika Onuki,Dai Aoki,Jacques Flouquet,Zachary Fisk 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.3
We report precision c-axis magnetic measurements on a high-quality single crystal of the heavyfermion metamagnet UCoAl. The metamagnetic transition at HM changes from 1st order at lowtemperature to a crossover at high temperature. HM is nearly linearly increasing with increasingtemperature up to a critical temperature T0. The critical temperature T0 is determined from boththe field and the temperature dependences of magnetization to be 11 K. The field dependence ofthe Sommerfeld coefficientis estimated from M(T) by using a Maxwell relation. (H) shows astep-like decrease at HM. This behavior is consistent with the previous reports of specific heat andresistivity measurements at low temperatures.
Hybridization gap and Fano resonance in SmB<sub>6</sub>
Rö,ßler, Sahana,Jang, Tae-Hwan,Kim, Dae-Jeong,Tjeng, L. H.,Fisk, Zachary,Steglich, Frank,Wirth, Steffen National Academy of Sciences 2014 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF Vol.111 No.13
<P>Hybridization between conduction electrons and the strongly interacting <I>f</I>-electrons in rare earth or actinide compounds may result in new states of matter. Depending on the exact location of the concomitant hybridization gap with respect to the Fermi energy, a heavy fermion or an insulating ground state ensues. To study this entanglement locally, we conducted scanning tunneling microscopy and spectroscopy (STS) measurements on the “Kondo insulator” SmB<SUB>6</SUB>. The vast majority of surface areas investigated were reconstructed, but infrequently, patches of varying sizes of nonreconstructed Sm- or B-terminated surfaces also were found. On the smallest patches, clear indications for the hybridization gap with logarithmic temperature dependence (as expected for a Kondo system) and for intermultiplet transitions were observed. On nonreconstructed surface areas large enough for coherent cotunneling, we were able to observe clear-cut Fano resonances. Our locally resolved STS indicated considerable finite conductance on all surfaces independent of their structure, not proving but leaving open the possibility of the existence of a topologically protected surface state.</P>
Pressure Evolution of the Metamagnetic Transition in UCoAl As Measured Using 59Co NMR
Hisashi Kotegawa,Hiroki Nohara,Hideki Tou,Tatsuma D. Matsuda,Etsuji Yamamoto,Yoshinori Haga,Zachary Fisk,Yoshichika Onuki,Dai Aoki,Jacques Flouquet 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.3
We have performed NMR measurements under pressure in UCoAl with a quantum critical endpointof the metamagnetic transition from the paramagnetic phase to the ferromagnetic (FM) phase. 59Co-NMR sensitively detects the evolution of the internal field caused by applying the externalfield. The metamagnetic field Hm increases with increasing pressure consistently with other experimentalmethods, accompanied by the suppression of the magnetization in the field-induced FMphase and the magnetization jump at Hm. The loss of the NMR signal on approaching the QCEPindicates the development of the spin fluctuations.
Shubnikov-de Haas Oscillation in PuIn3
Yoshinori Haga,Eric D. Bauer,Paul H. Tobash,Jeremy N. Mitchell,Oscar Ayala-Valenzuela,Ross D. McDonald,Charles H. Mielke,Zachary Fisk 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.3
The Fermi surface of PuIn3 is investigated using flux-grown single crystals. Shubnikov-de Haas(SdH) oscillations were detected by means of the skin-depth measurement using a proximitydetector-oscillator circuit. Angular dependence of the SdH frequency which corresponds to theextremal cross-sectional area of Fermi surface agrees well with the previous magnetic susceptibilitymeasurement using conventional field-modulation method. The SdH oscillation suddenly vanisheswhen the magnetic field is tilted from the cubic [111] direction.