top of page

Anomalous metallic behavior and exotic superconductivity

in strongly correlated materials

Simple on its own

Gather, a realm of wonder

More is different

One might think that the best way to deal with an extremely complex problem is to break it into small parts and study how each part work. However, many real-world challenges refuse this approach. All too often, macroscopic scale behavior takes the form of "emergent' properties" that are completely beyond our imagination based on the knowledge of an individual building block. Indeed, there is nothing in a single water molecule that can guide us to predict the snowflake’ dazzling variety of pattern; our understanding of brain cells is far from enough for comprehending human consciousness – we are surrounded by fascinating emergent properties, which seek universal organizing principles that link the enigmatic interaction network in the microscopic realm with descriptions at the macroscopic level.

In condensed matter physics, the emergent phenomena involve the beautiful and mind-boggling aspects of quantum mechanics. A celebrated example is the high-temperature superconductivity: the strong correlation among electrons massively entangles the spin, orbital, and charge degrees of freedoms, leading to dissipationless charge transport at surprisingly high temperatures and novel quasiparticles that are radically different from the underlying electrons. With its fundamental significance and prospects for technological innovations, the discovery of the high-temperature superconductivity sparks a tremendous expansion of quantum materials research that branches out into various fronts. Yet, the origin of the high-temperature superconductivity remains an open question despite decades of research effort. Quite often, exotic SC appears near the non-Fermi-liquid (NFL) or strange metal phase - a highly entangled electronic state featuring a complete breakdown of the quasiparticle picture and singular behavior of physical properties. Understanding the NFL may hold the key to unveiling the primary driver of unconventional superconductivity and a wide variety of quantum states in condensed matter systems.

By combining material synthesis, high-precision measurements under extreme conditions, and a global collaborative network involving world-leading experts, our group's research leads the way to establishing new paradigms in quantum material research. We discovered the first Yb-based heavy-fermion superconductor and demonstrated an intimate connection between the exotic superconductivity and the quantum criticality of valence fluctuations. Another highlight is the multipolar Kondo material, in which conduction electrons interact strongly with local moments carrying high-rank quadrupoles and octupoles but no magnetic dipole. Such a system opens a new horizon for exploring spin-orbital entangled quantum phases and exotic SC. Please feel free to check out the following selected publications for an in-depth exploration of topic.

[1] Y. Shimura et al., Phys. Rev. Lett. 122, 256601 (2019).

[2] M. Tsujimoto et al., Phys. Rev. Lett. 113, 267001 (2014).

[3] K. Matsubayashi et al., Phys. Rev. Lett., 109, 187004 (2012).

[4] A. Sakai and S. Nakatsuji, J. Phys. Soc. Jpn., 80, 063701 (2011).

[5] S. Nakatsuji et al., Nat. Phys., 4, 603 (2008).

[6] T. Matsumoto et al., Science, 331, 316 (2011).

[7] T. Tomita et al., Science, 349, 506 (2015).

[8] K. Kuga et al., Science Adv., 8, 3547 (2018).


Image of electric quadrupolar Kondo effect and superconductivity.

Related research

4. 強相関電子系の異常金属相と非従来型超伝導



一方、電子相関の強い、「強相関電子系」では、もはや、一体近似は成り立たず、アボガドロ数の電子間の相関をすべて取り扱う必要が出てきます。そのため、現状の理論手法では太刀打ちできず、様々な近似法で理解を進める動きがあります。そのなかで、この分野を主導しているのは実験によるその多彩な量子相の解明です。特に、金属の電子論の構築に重要な現象に、強相関電子系における、(一体近似による)準粒子描像が成り立たない「異常金属(Strange Metal)」やBCS理論に従わない「非従来型超伝導」など非自明な現象が多くあります。これらは高温超伝導機構と関係しているだけでなく、量子臨界現象を通じてブラックホールなどの一般相対論と関係があることがわかってきています。






[1] Y. Shimura et al., Phys. Rev. Lett. 122, 256601 (2019).

[2] M. Tsujimoto et al., Phys. Rev. Lett. 113, 267001 (2014).

[3] K. Matsubayashi et al., Phys. Rev. Lett., 109, 187004 (2012).

[4] A. Sakai and S. Nakatsuji, J. Phys. Soc. Jpn., 80, 063701 (2011).

[5] S. Nakatsuji et al., Nat. Phys., 4, 603 (2008).

[6] T. Matsumoto et al., Science, 331, 316 (2011).

[7] T. Tomita et al., Science, 349, 506 (2015).

[8] K. Kuga et al., Science Adv., 8, 3547 (2018).



bottom of page