Ibaraki UniversityCore Research Group for Structural Physics

1. Novel functional material development by high pressure synthesis

Sometimes we can obtain the materials which can be produced only under high-pressure circumstance. The pressure reaches 250,000 atm at 600 km deepness of the earth. The bottom picture is the equipment which can realize such environment. We have succeeded in synthesis of novel rare-earth borides such as GdB₁₂ and SmB₁₂ which cannot be produced up to date. At present we are challenging the high-pressure synthesis of other lighter rare earth borides and new organic compounds.

2. Research on exotic physical properties of Kondo insulator in rare-earth borides

Pure and large single crystals have been grown by the floating-zone method using the 4-zenon-lamp image furnace and their physical properties have been evaluated. SmB₆ and YbB₁₂ called Topological Kondo Insulator are taken much attention as the candidates of future-high response device. Their bulk properties such magnetism, transport and thermal properties and surface-state are evaluated. Recently quantum oscillation phenomenon which is observed only in metallic compounds under high magnetic field has been discovered in semiconductor YbB₁₂.This phenomenon is also taken attention as a very serious academic problem among the world because this is concern the definition of both metal and insulator.

1. Search for Weyl semimetals in rare-earth strongly correlated electron systems with chiral symmetry

Electrons characterized by the Wyle solution of the relativistic theory are expected to appear in materials without inversion symmetry. We are searching Weyl fermions, which have been investigated worldwide, in Kondo-semimetal systems with a chiral symmetry shown in the right figure.

2. High-rank electron multipole order and effects on transport phenomena

An electron is characterized by charge, spin, and orbital motion in an atom. These degrees of freedom also cause high-rank multipoles (charge and magnetic). We have investigated the multipole ordered state shown in the left figure in rare-earth intermetallics, which are relevant to electronic transport anomalies.

3. Quantum criticality in anharmonic atomic motions and spin fluctuation in the vicinity of phase transformation

Crystal and magnetic structure transformations accompany anharmonic atomic vibration and anomalous spin fluctuation. We are searching novel quantum criticality caused by such peculiar dynamics using quantum beam instruments.

1. Local Atomic Structure Investigations by White Neutron Holography in J-PARC

Our group has succeeded in developing novel technique, white neutron holography, in Ibaraki Univ., which is the unique probe to observe atomic structures around dopants in functional materials.

2. Magnetic correlations of Rare earth compounds and strongly correlated electron systems

Our group is investigating physical properties of rare earth compounds, which reveals anomalous magnetic and transportation properties, by neutron scattering.

3. Development of novel techniques using white pulsed neutrons

Neutron beam is a quite effective probe to observe atoms and magnetic moments. Our group is developing world-first novel techniques for observations of atoms using neutrons in J-PARC.

1. Magnetism in strongly correlated electron systems

We are experimentally studying the magnetic and structural properties in strongly correlated electron systems such as rare-earth and actinide compounds mainly by using neutron and x-ray scattering techniques.

1. Correlated s-electron systems of alkali metal nanoclusters arrayed in zeolite crystals

Zeolites are porous aluminosolicate crystals possessing regularly arrayed nanospaces (cages) with rich varieties of structure. Alkali-metal nanoclusters can be generated by the loading of guest alkali atoms into the regular nanospaces. Because of the new quantum states of confined s-electrons, the electron correlation, and also the electron-phonon interaction, exotic physical properties such as magnetic orderings (ferromagnetism, antiferromagnetism, ferrimagneism) and insulator-to-metal transitions have been found depending on the host crystal structure, the species of alkali element and the electron concentration. We synthesize these new materials and perform various experiments such as optical spectroscopy, magnetic measurements, electron spin resonance, muon spin rotation/relaxation, neutron diffraction etc. in order to clarify the mechanism of those exotic properties.

Interplay between quantum critical behavior and superconductivity in heavy-fermion systems

The heavy fermion superconductor CeCoIn₅ exhibits clear signatures of quantum critical fluctuations near the superconducting upper critical field H_c2, but their origin is still unresolved because relevant magnetic order has not yet been identified in this compound. We have recently demonstrated an emergence of new field-induced antiferromagnetic order coupled with quantum critical fluctuations in Zn-doped CeCoIn₅. Scaling analysis for the specific heat data of Zn-doped CeCoIn₅ suggests that the quantum critical fluctuations seen in pure and Zn-doped CeCoIn₅ have almost the same origin; the quantum critical fluctuations enhanced near H_c2 in pure CeCoIn₅ originate from the "hidden" order parameter of the field-induced antiferromagnetic phase observed in Zn-doped CeCoIn₅.

2. Heterogeneous magnetism and its dynamics in 4d and 5d transition-metal oxides with metal-insulator transition

The 4d and 5d electrons in the transition-metal oxides often behave as the itinerant conduction electrons. However, strong electronic correlations may lead to an instability of metal-insulator transition and then yield anomalous electronic state involving both the itinerant and localized characteristics. Our investigations for itinerant ferromagnet SrRuO₃ and its doped alloys have revealed that these alloys exhibit unusual quantum spin states at low temperatures originating from the 4d electrons with the itinerant-localized dual nature.