Heat capacity peak at the quantum critical point of the transverse Ising magnet CoNb2O6

Tian Liang, S. M. Koohpayeh, J. W. Krizan, T. M. McQueen, R. J. Cava, N. P. Ong

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The transverse Ising magnet Hamiltonian describing the Ising chain in a transverse magnetic field is the archetypal example of a system that undergoes a transition at a quantum critical point (QCP). The columbite CoNb2O6 is the closest realization of the transverse Ising magnet found to date. At low temperatures, neutron diffraction has observed a set of discrete collective spin modes near the QCP. Here, we ask if there are low-lying spin excitations distinct from these relatively high-energy modes. Using the heat capacity, we show that a significant band of gapless spin excitations exists. At the QCP, their spin entropy rises to a prominent peak that accounts for 30% of the total spin degrees of freedom. In a narrow field interval below the QCP, the gapless excitations display a fermion-like, temperature-linear heat capacity below 1K. These novel gapless modes are the main spin excitations participating in, and affected by, the quantum transition.

Original languageEnglish (US)
Article number7611
JournalNature communications
StatePublished - Jul 6 2015

All Science Journal Classification (ASJC) codes

  • General Chemistry
  • General Biochemistry, Genetics and Molecular Biology
  • General Physics and Astronomy


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