Unconventional Transport of Spin Bipolarons on an Antiferromagnetic buckled hexagonal lattice of half-filled $d$-band Mn$^{2+}$ ions

ORAL

Abstract

CaMn$_2$Sb$_2$ presents a magnetic system with a buckled hexagonal lattice of half-filled $d$-band Mn$^{2+}$ ions. AC resistivity and susceptibility exhibit non-monotonic temperature dependence at 85-210~K. Below 85~K it has an antiferromagnetic (AF) phase with an activation energy of 28~meV, and above 210~K a paramagnetic phase. Using Raman spectroscopy we find a mode at 32~meV which develops below the AF transition. We attribute this excitation to the activation energy associated with the motion of spin bipolarons. Here, hybridization between Sb and Mn results in extra electrons for the Mn 3$d$-shells. It is energetically favorable for these extra carriers to form spin-singlets. These spin-bipolarons cover two Mn sites with a binding energy of $\sim$80~meV and conduction proceed via photo-assisted hopping with an activation energy of $\sim$32~meV. This spin bipolaron model explains the spectroscopic features providing a self-consistent picture of this conductivity mechanism that also clarifies reported unusual temperature-dependent magnetic and transport data.

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Authors

  • Verner Thorsmolle

    Rutgers, The State University of New Jersey

  • Alexander Ignatov

    Rutgers, The State University of New Jersey

  • Maria Pezzoli

    Rutgers, The State University of New Jersey

  • K. Haule

    Rutgers, The State University of New Jersey, Rutgers University, Dept. Physics, Rutgers University, Department of Physics and Astronomy, Rutgers University

  • David Kolchmeyer

    Rutgers, The State University of New Jersey

  • Alexander Lee

    Rutgers, The State University of New Jersey

  • Jack Simonson

    Stony Brook University, Department of Physics and Astronony, Stony Brook University, Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794

  • Meigan Aronson

    Stony Brook University, Brookhaven National Laboratory, Stony Brook University and Brookhaven National Laboratory, Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794

  • Girsh Blumberg

    Rutgers, The State University of New Jersey