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Superconductivity and Magnetism in Selected Filled Skutterudites and Heavy Fermion Systems

Adhikari, Ram Bahadur
http://rave.ohiolink.edu/etdc/view?acc_num=kent16173874994732

Abstract Details

2021, PHD, Kent State University, College of Arts and Sciences / Department of Physics.
Strongly correlated electron systems constitute a rich reservoir for interesting physical phenomena. The competition and interplay between the localized magnetic moments in partially filled d or f electron systems and the itinerant conduction electrons states lead to novel phenomena such as complex magnetic properties, unconventional superconductivity, non-Fermi-liquid behavior, and the coexistence of superconductivity and magnetism. Such intriguing physical phenomena can be achieved by tuning the system with a control parameter, such as chemical composition, applied pressure, and magnetic field. It is interesting to study the chemical substitution effects on the correlated f electron system along with magnetic field to explore their complex phase diagram. This dissertation work focuses on experimental studies of the Ce and Eu substituted filled skutterudite system PrPt4Ge12 over a wide range of doping, magnetic field, and temperature using heat capacity measurements. The first study will focus on the specific heat and electrical resistivity measurements performed on the Pr1-xCexPt4Ge12 crystals. We have found that Ce monotonically suppresses the superconducting transition temperature Tc and a small Ce concentration of x = 0.14 brings the Tc to as low as 0.6 K. We further have demonstrate that small Ce substitution does not affect the multiband nature of superconductivity seen previously in the parent compound PrPt4Ge12. On the other hand, our data provide evidence that one of the two gaps is nodal in the parent compound and that Ce substitution gradually suppresses the value of the nodal gap. To understand the possible interplay between superconductivity and magnetism, we study the same parent system PrPt4Ge12, this time substituting Pr with europium. The compound so formed is Pr1-xEuxPt4Ge12 whose end members are superconductor (x = 0) and antiferromagnetic (x = 1) at lower temperatures, so that there is the possibility of interaction between superconductivity and magnetism in the intermediate doping range. The increase of Eu concentration leads to a suppression of the superconducting transition temperature as in the case of cerium substitution. There is a low temperature heat capacity anomaly present over the whole doping range. Our analysis of the heat capacity data shows that in alloys with x ≤ 0.5 the Schottky peaks in the heat capacity in the superconducting state appear to be due to Zeeman splitting by an internal magnetic field. Our theoretical analysis suggests that this internal magnetic field is a result of short-range antiferromagnetic correlations between the europium ions. We further investigated the effect of Eu substitution on the Pr site through heat capacity measurements on the same system in an applied magnetic field. The low temperature heat capacity peaks seen in the samples with x ≤ 0.5 shift to higher temperatures with increasing magnetic field. For the samples with x > 0.5, the Schottky anomaly peaks shift to lower temperature with increasing external field Hex. Currently, we do not have a universal understanding to the breakdown of the Fermi-Liquid (FL) behavior in f electron materials. There is some evidence suggesting that the breakdown of the FL behavior and the unconventional superconducting (SC) pairing could be the result of a zero-temperature phase transition taking place at a quantum critical point (QCP). The final project included in this dissertation is the discussion of the QCP using the results of specific heat, electrical resistance, and magneto-resistivity measurements on single crystals of the heavy-fermion superconducting alloy Ce0.91Yb0.09CoIn5. We observed the signatures of the non-Fermi-liquid to Fermi-liquid crossover in the temperature dependence of the Sommerfeld coefficient γ and the resistivity data in high applied magnetic fields. We also show that the Yb-doped samples with x= 0.09 exhibit universality due to an underlying quantum phase transition without an applied magnetic field by utilizing the scaling analysis of γ. The quantum critical point is antiferromagnetic in nature as shown by the fitting of the heat capacity and resistivity data based on the existing theoretical models.
Carmen Almasan (Advisor)
Maxim Dzero (Committee Member)
Almut Schroeder (Committee Member)
Mietek Jaroniec (Committee Member)
Songping Huang (Committee Member)
128 p.
Physics
Heavy Fermions, Filled Skutterudies, Schottky Anomaly, Quantum Criticality, Superconductivity, NFL behavior, Superconducting Energy Gap

Recommended Citations

Citations

  • Adhikari, R. B. (2021). Superconductivity and Magnetism in Selected Filled Skutterudites and Heavy Fermion Systems [Doctoral dissertation, Kent State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=kent16173874994732

    APA Style (7th edition)

  • Adhikari, Ram. Superconductivity and Magnetism in Selected Filled Skutterudites and Heavy Fermion Systems. 2021. Kent State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=kent16173874994732.

    MLA Style (8th edition)

  • Adhikari, Ram. "Superconductivity and Magnetism in Selected Filled Skutterudites and Heavy Fermion Systems." Doctoral dissertation, Kent State University, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=kent16173874994732

    Chicago Manual of Style (17th edition)

kent16173874994732
330
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This open access ETD is published by Kent State University and OhioLINK.