ISSP - The institute for Solid State Physics

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Takigawa Group

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We use nuclear magnetic resonance (NMR) as the major experimental tool to investigate exotic phenomena caused by strong electronic correlation in solids. A remarkable feature of strongly correlated electron systems is the competition among various kinds of ordering such as superconductivity, ferro- or antiferromagnetism, charge and orbital order. Quantum phase transitions between these ground states can be caused by changing the external parameters such as magnetic field or pressure. Nuclei have their own magnetic dipole and electric quadrupole moments, which couple to the magnetic field or electric field gradient produced by surrounding electrons. This makes NMR a powerful local probe for microscopic investigation of the exotic order and fluctuations of multiple degrees of freedom of electrons, i.e., spin, charge and orbital. We use various NMR spectrometers in different environment (low temperature, high magnetic field and high pressures) to investigate transition metal compounds, rare earth compounds, and organic solids.

NMR spectra of Al nuclei in PrTi2Al20H at the temperature of 60K and the magnetic field of 6.6 tesla. The Pr ions with a non-magnetic doublet ground state in the crystal electric field undergo ferro-quadrupole order at low temperatures. There are three Al sites forming a cage surrounding Pr ions, each of which splits into inequivalent sites under magnetic fields along <111> or <100>. Each Al site generates five quadrupole split NMR lines, resulting in a complicated NMR spectrum.
The NMR lines split below 2K under the magnetic field along <111> due to ferro-quadrupole order. The signals from the 3a sites are indicated by the red box.
The splitting of NMR lines uniquely determines the symmetry of the charge density distribution and the order parameter.

Research Subjects

  1. Dynamics and quantum phase transitions in low dimensional or frustrated spin systems
  2. Exotic superconductors
  3. Ordering and fluctuations of charge, orbital, and multipoles in strongly correlated electron systems
  4. Novel orders in spin-orbit coupled electron systems