Unveiling structure-function relationships in intermetallic quantum materials

Event Date:
2026-01-22T13:00:00
2026-01-22T15:00:00
Event Location:
Brimacombe Room 311
Speaker:
Samikshya Sahu, Final Doctoral Defense
Related Upcoming Events:
Grad Theses
Intended Audience:
Faculty
Local Contact:

All are welcome to see this defense!

Event Information:

 

Abstract:

Traditionally, crystal growers have sought to make materials with perfect crystallinity, free from defects and lattice imperfections. 
However, real materials always exhibit some degree of defects or disorder, and in some cases, these imperfections can dramatically alter their properties. In this thesis, we explore the crystal growth, structural, magnetic, and electronic properties of three families of quantum materials in which crystalline defects play a crucial role.

The first material family we explore is $M$Sn$_4$, in which \ce{PtSn4} stands out as having unique electrical transport features, including a high residual resistivity ratio (RRR), a key metric for quantifying intrinsic defects in metals. Our results indicate that the transport features in \ce{PtSn4} are related to an unusually low defect density, as proved using the aid of electrical transport measurements, scanning tunnelling microscopy (STM) and density functional theory (DFT) calculation. Our work demonstrates that the crystal chemistry in \ce{PtSn4} exemplifies a structural Goldilocks effect, where the naturally defect-intolerant Pt and Sn layers support high electron mobilities.

Secondly, we study the evolution of the magnetic ground state in \ce{NdRh2Ge2} as a function of temperature and magnetic field. 
\ce{NdRh2Ge2} shows a cascade of metamagnetic transitions, including both commensurate and incommensurate magnetic states. Additionally, a unique Hall anomaly is observed, which originates from the coexistence of magnetic phases. This study highlights the intricate relationship between single-ion anisotropy, electronic structure, and magnetic order, as well as the influence of magnetic defects on properties.

Lastly, we characterize the Remeika phases \ce{Nd3Rh4Ge13} and \ce{Nd3Ir4Ge13}. The crystal structures of the phases are verified using powder x-ray and single crystal x-ray diffraction. Additionally, we observe antiferromagnetic ground states and metamagnetic transitions emerging from the ordered states. These systems enabled us to investigate the effect of Ge vacancies, which appear to be strongly coupled to structural distortions resulting in lower symmetry structures. All these examples highlight the importance of studying material properties in the context of their defects or disorder.
 

Add to Calendar 2026-01-22T13:00:00 2026-01-22T15:00:00 Unveiling structure-function relationships in intermetallic quantum materials Event Information:   Abstract: Traditionally, crystal growers have sought to make materials with perfect crystallinity, free from defects and lattice imperfections. However, real materials always exhibit some degree of defects or disorder, and in some cases, these imperfections can dramatically alter their properties. In this thesis, we explore the crystal growth, structural, magnetic, and electronic properties of three families of quantum materials in which crystalline defects play a crucial role. The first material family we explore is $M$Sn$_4$, in which \ce{PtSn4} stands out as having unique electrical transport features, including a high residual resistivity ratio (RRR), a key metric for quantifying intrinsic defects in metals. Our results indicate that the transport features in \ce{PtSn4} are related to an unusually low defect density, as proved using the aid of electrical transport measurements, scanning tunnelling microscopy (STM) and density functional theory (DFT) calculation. Our work demonstrates that the crystal chemistry in \ce{PtSn4} exemplifies a structural Goldilocks effect, where the naturally defect-intolerant Pt and Sn layers support high electron mobilities. Secondly, we study the evolution of the magnetic ground state in \ce{NdRh2Ge2} as a function of temperature and magnetic field. \ce{NdRh2Ge2} shows a cascade of metamagnetic transitions, including both commensurate and incommensurate magnetic states. Additionally, a unique Hall anomaly is observed, which originates from the coexistence of magnetic phases. This study highlights the intricate relationship between single-ion anisotropy, electronic structure, and magnetic order, as well as the influence of magnetic defects on properties. Lastly, we characterize the Remeika phases \ce{Nd3Rh4Ge13} and \ce{Nd3Ir4Ge13}. The crystal structures of the phases are verified using powder x-ray and single crystal x-ray diffraction. Additionally, we observe antiferromagnetic ground states and metamagnetic transitions emerging from the ordered states. These systems enabled us to investigate the effect of Ge vacancies, which appear to be strongly coupled to structural distortions resulting in lower symmetry structures. All these examples highlight the importance of studying material properties in the context of their defects or disorder.  Event Location: Brimacombe Room 311