Harnessing Unique Quantum Effects with Cutting-Edge Techniques

Quantum materials

In our group, we create materials and nanoscale devices that show unique quantum-physical effects. We focus on heavy-element semiconductors like InSb and PbTe, which have special properties making them perfect for experiments with low-dimensional effects. To grow these materials, we use advanced techniques like metal-organic vapor-phase epitaxy and molecular beam epitaxy, to maximize the crystalline quality, purity and structural complexity of our materials and devices.

Our Achievements and Future Goals

  • Majorana Fermions: We've successfully proven the existence of Majorana fermions at the interface of an InSb nanowire with a superconductor. This is a significant step towards using these particles in quantum computing.
  • Improving Interfaces: We've enhanced the superconductor-nanowire interface to make it more transparent, which is crucial for better device performance.
  • Complex Nanowire Networks: We're working on growing complex nanowire networks with in-situ-deposited superconducting islands to enable the braiding of Majorana particles, a key process for quantum computation.
  • Topological Insulators: We're also exploring materials with nontrivial band topology, known as topological insulators, which could form Majorana particles without an external magnetic field.

Our ultimate goal is to use these advanced materials and techniques to develop practical quantum computing components.

Discovering the Future: Topological Quantum Materials and 2D Quantum Materials

To follow our achievements and future goals we are exploring both topological quantum materials as 2D quantum materials. 

Topological Quantum Materials

In our research, we focus on Topological Crystalline Insulators (TCIs) to create topological qubits that resist external noise. TCIs are unique materials with special 2D states on their surface, resembling the properties of Dirac particles and showing helical spin patterns. These states are protected by the crystal's mirror symmetries, allowing us to control them with strain or electric fields. This control can even produce higher-order topological insulators (HOTIs) with 1D states. For reference, see figure 1. 

In our lab, we explore these properties using PbSnTe nanowires, which we grow using Molecular Beam Epitaxy. We then create nanoscale devices from these nanowires in the 果冻传媒 Nanolab cleanroom. These devices are tested at very low temperatures in our Quantum Transport Lab to reveal their quantum behaviors. For reference, see figure 2.

In summary, topological qubits represent a cutting-edge approach in the quest for robust and scalable quantum computers, leveraging the principles of topology to provide natural error resistance and long-term stability.

Figure 1: Three terminal nanowire device, with a Pb_0.5_Sn_0.5_Te nanowire in green, normal metal (NM) contacts in gold, and ferromagnetic (FM) tunnel junction in red. A current is injected with via the NM contacts, and the FM tunnel junction is used to measure the spin polarization of the surface states.
Figure 2: Four terminal nanoflake device. By performing Hall measurements in the 鈥榲an der Pauw鈥� geometry, the carrier density in the nanoflake can be determined

Two-Dimensional Quantum Materials

We also study materials with a layered crystal structure, where layers interact weakly, allowing us to isolate individual layers as thin as a single atom (~0.3 nm). Examples of these materials include graphene (a semimetal), MoSe2 (a semiconductor), and Bi2Se3 (a topological insulator). By stacking different layers, we can create "Van der Waals" heterostructures, adding another level of design flexibility by adjusting the twist angle between layers. For reference see figure 3. 

These layered materials and their combinations exhibit remarkable properties such as extremely high charge mobility, excellent thermal conductivity, and strong light-matter interactions.

In the Ultrafast Dynamics in Nanoscale Systems (UDNS) group (), we study these fundamental properties and explore their potential applications in (opto)electronic and thermal devices, such as ultrafast photodetectors and heat dissipators.

In our Ultrafast Optoelectronics Lab, we prepare samples and devices from these materials. We perform precise optical, electronic, and optoelectronic measurements using custom-built setups with exceptional spatial (nanometer) and temporal (femtosecond) resolution.

Figure 3: Suspended flakes of MoSe2 with varying thickness from monolayer (1L) to 70 layers (70L), suspended over a hole with a diameter of 15 渭m. We prepared these record-large suspended samples in our lab using exfoliation and dry transfer. For more information, see [link: J. Phys. Mater. 4 046001 (2021)].