## Scholarships

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Lecturer

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Bom Soo Kim received his Ph.D. in 2009 from the University of California at Berkeley. He was a joint postdoc at IESL-FORTH and University of Crete working together with an experimentalist (high-temperature superconductivity) and a string theorist. He worked as a postdoctoral fellow at Tel Aviv University and as a teaching postdoc at the University of Kentucky before joining Loyola University Maryland as a full time Lecturer on Fall 2017.

**A. Magnetic Skyrmions and Hall Transport :**

Magnetic Skyrmions are topological objects (protected by a topological number and an energy gap and robust under disturbances) that have been originally proposed in high energy theory, yet recently observed in real condensed matter systems. They have a viable application as a next generation storage devices and have been actively studied theoretically and experimentally. Due to extended nature of the Skyrmions, most of the studies rely on phenomenological models.

There is so-called Ward identities that only rely on symmetries present in the system and thus conservation equations. We have generalized this to derive a more powerful set of Ward identities that captures the effects of topological charge on 2+1 dimensions in http://arxiv.org/abs/1506.08199 (Phys. Rev. Lett. 117, 116805 (2016)). From mathematical point of view, the contribution of the topological charges comes from a central extension in momentum momentum correlator, which can not be captured by conservation equations.

We provide several experimental signatures. For example, the thermal Hall conductivity is directly related to the topological charge density of Skyrmions when the system is insulating. This relation is further extended in the presence of a magnetic field and a conserved current. Interestingly, the topological charge density produces a distinct signature in the electric Hall conductivity, which is identified in existing experimental data.

We emphasize that the Hall Viscosity can play an important role in the magnetic Skyrmion experiments. We propose a simple and clear way to measure the Hall viscosity once the thermal Hall conductivity is measure as a function of momentum. For insulating materials with translation invariance, the Hall viscosity is nothing but the Skyrmion density multiplied by the ratio between the slope (numerator) and intercept (denominator) at zero momentum! We also provide a similar relation to the conducting materials in the presence of charge carriers as well.

- Measuring Hall Viscosity in Magnetic Skyrmion systems
- Ward Identity and Parity-odd Phenomena

**B. Holography, Quantum field theory and String theory :**

String theory aspires to unify the four fundamental interactions of nature. Despite various successes, the theory has yet to bring relevance to real experiments. Holography, a precise one-to-one map from a weakly-coupled classical gravity in Anti de-Sitter space to a strongly-coupled conformal field theory living on its boundary that is embraced in string theory, provides one of the most promising possibilities, especially, through the application to condensed matter physics. This program has experienced various successes in condensed matter applications, an integrated and basic guiding principle has yet to be established. One of my goals is to understand the universal low energy physics of holographic backgrounds and to provide testable predictions for condensed matter physics. Inevitably, this will provide deeper understanding of holography and string theory. Some of my research topics include

- Holographic Renormalization of Einstein-Maxwell-Dilaton theories
- Effective Holographic Theories
- Hydrodynamics and Quantum Criticality
- Non-Equilibrium Critical Phenomena: Aging

**C. Selected Talks :**

- “Skyrmions and Hall viscosity,” Invited talk at the 62nd Annual Conference on Magnetism and Magnetic Materials (MMM), Pittsburgh, Pennsylvania, November 6-10, 2017.
- “Entanglement Entropy with Current and Chemical potential.,” May 2017 at the Great Lakes Strings Conference, University of Cincinnati, Cincinnati, USA.
- “Skyrmion charge, Ward identity and Hall transport,” Oct. 2015 at SPOCK regional string meeting, University of Cincinnati, Cincinnati, USA.
- “Hall Transport for Skyrmions,” May 2015 at Korea Institute for Advanced Study (KIAS), Seoul, Korea.
- “Parity breaking transports and Ward identities in 2+1 dimensions,” Mar. 2015 at the Great Lakes Strings Conference, University of Michigan, Ann Arbor, USA.
- “Lifshitz Hydrodynamics and its application to quantum critical region,” Mar. 2015 at University of California at Berkeley, Berkeley, USA.
- “Universal hydrodynamic description of quantum critical points with Lifshitz scaling,” July. 2013 at Kavli IPMU, University of Tokyo, Kashiwa, Japan.
- “Charged Dilatonic Black Holes and their thermodynamic and transport Properties,” July 2010 at ICTP, Trieste, Italy.
- “Transport properties of high Tc superconductor at very low temperature and AdS/CFT,” June 2011 at the Sixth Crete Regional Meeting in String Theory, Milos, Greece.
- “Charged Dilatonic Black Holes and their Transport Properties,” June 2010 at the XVIth European Workshop on String Theory, Madrid, Spain.

**D. Selected Publications : (full publication list)**

- B. S. Kim, "Entanglement Entropy with Background Gauge Fields," JHEP 1708, 041 (2017). arXiv:1706.07110 [hep-th].
- B. S. Kim, "Entanglement Entropy, Current, and Chemical Potential," arXiv:1705.01859 [hep-th].
- B. S. Kim, "Holographic Renormalization of Einstein-Maxwell-Dilaton Theories," JHEP 1611, 044 (2016). arXiv:1608.06252 [hep-th].
- B. S. Kim and A. Shapere, “Skyrmions and Hall Transport,” Phys. Rev. Lett. 117, 116805 (2016). [arXiv:1506.08199 [cond-mat.str-el]]
- C. Hoyos, B. S. Kim and Y. Oz, “Ward Identities for Hall Transport,” JHEP 1410, 054 (2014). [arXiv:1407.2616 [hep-th]]
- C. Hoyos, B. S. Kim and Y. Oz, “Lifshitz Field Theories at Non-Zero Temperature, Hydrodynamics and Gravity,” JHEP 1403, 029 (2014). [arXiv:1309.6794 [hep-th]]
- C. Hoyos, B. S. Kim and Y. Oz, “Lifshitz Hydrodynamics,” JHEP 1311, 145 (2013). [arXiv:1304.7481 [hep-th]]
- B. S. Kim, “Schroedinger Holography with and without Hyperscaling Violation,” JHEP 1206, 116 (2012). [arXiv:1202.6062 [hep-th]]
- B. S. Kim, E. Kiritsis and C. Panagopoulos, “Holographic quantum criticality and strange metal transport,” New J. Phys. 14:043045 (2012). [arXiv:1012.3464 [cond-mat.str-el]]
- C. Charmousis, B. Gouteraux, B. S. Kim, E. Kiritsis and R. Meyer, “Effective Holographic Theories for low-temperature condensed matter systems,” JHEP 1011, 151 (2010).[arXiv:1005.4690 [hep-th]]

$40,000 Scholarships are available in physics with CPaMS Scholars