Quantum Materials

Computational platform “lsquant”

On the modelling side, the ICN2 has launched a computational platform (lsquant.org) to promote advanced in-house simulation tools, which allow accessing quantum transport properties in quantum materials of arbitrary structural and chemical complexity. The platform will also serve as flagship initiative to engage enlarged partnerships with companies and individuals interested in developing and using efficient computational tools giving unique access to quantum materials properties.

Quantum information transduction

The ICN2 quantum materials task force is exploring novel approaches for quantum information transduction and communication using a combination of topological materials for advanced quantum devices. The main objective is to discover efficient ways to generate, transport, manipulate, store and detect quantum information over on-chip propagation scales, by taking advantage of the resilience to decoherence of tokens of information based on chosen materials. This is achieved using suitable topological states in lab-size devices, obtained by means of scalable fabrication protocols. As an example, studies are devoted to achieving transduction of quantum information by mixing photons sources together with excitonic and magnonic states generated in quantum materials-based devices, manipulated by designing suitable circuit architecture and using device electrostatic control.

Topological phononics

Phonons, which are quanta of lattice vibrations, are ubiquitous and usually undesirable as being responsible for decoherence and noise. At the same time, they have one of the lowest energy as excitations in matter and hold a promise for low energy information processing, in the zone of overlap between quantum and classical energy transport. Researchers at the ICN2 are exploring the degree to which information carried by phonons can be made robust to dissipation applying concepts of topological protection of lattice vibrations.

Topological photonics

A long-standing aim in integrated classical and quantum photonics is the incorporation of light sources in photonic resonators to enhance their emission efficiency. For this, phonons need to be harvested in a controlled manner by, for example, coupling an emitter to a slow-light photonic waveguide, where the group velocity of light may be orders of magnitude slower than the vacuum speed propagation. In this way, two functionalities are obtained simultaneously: emission efficiency enhancement and coupling of the emitted photons directly to already integrated propagating photonic modes. The downside is that these waveguides are extremely sensitive to fabrication disorder, seriously limiting the light propagation distance. Topological photonics is a possible solution to this challenge, extending the concepts and their realisation from topological insulators to bosons. The main goal is to design, fabricate and measure waveguides with minimum group velocity and backscattering losses with embedded quantum light emitters. These systems are scalable and amenable to integration with light sources, actuators and detectors to simultaneously transmit and actuate on optical signals.

Spintronics

Spintronics exploits the electron’s spin degree of freedom, in addition to the usual state of charge, to store, process and read information, but with the target of achieving lower power consumption of memory and logic components. The ICN2 explores forefront research on the potential of 2D materials-based van der Waals heterostructures and topological matter (topological insulators, Weyl semimetals, magnetic TI, etc..) for future spintronic applications. The main objectives are to demonstrate more energy-efficient mechanisms to generate pure spin current (through the so-called spin Hall effect) and spin-orbit torque components able to switch the magnetization of magnetic materials in a fast and reliable way. Currently, research in spintronics at the ICN2 includes growth and characterization of magnetic topological insulators and 2D materials such as graphene, MoS₂, PtSe₂, WSe₂ and hybrid 2D heterostructures.

Besides, at the ICN2 we investigate the frontier of quantum entanglement in topological matter and the opportunities to control and manipulate entanglement sources between intraparticle and interparticle degrees of freedom, to produce a novel paradigm for quantum computation in the long term.

Atomic scale characterization of quantum materials

The ICN2 holds a strong and long-term collaboration with Microsoft Quantum labs to develop hybrid superconductor-semiconductor quantum networks for scalable Majorana-based quantum computing circuits. In addition, we work on the atomic resolution STEM-based characterization and modeling of 1D, 2D and 3D nanomaterials exhibiting quantum properties (such as nanoflakes, nanosheets, quantum dots, 2DEG, nanowires, etc.).

Nanostructured graphene

By means of nano-structuring it is possible to imprint in graphene new properties, such as confinement gaps, 1D magnetism, or topologically protected states. Due to the single layer nature of this archetypal 2D material, any induced quantum property can be easily perturbed by external stimuli, including strain, electric and magnetic field, and chemical functionalization. Such sensitivity opens up new avenues for engineering quantum properties but also imposes strong limitations on their control. At the ICN2 we address this issue by fabricating graphene nanoarchitectures with atomic precision to control their pristine quantum properties. The response to external perturbations is studied locally, with the same atomic resolution, by scanning probe microcospy. Phenomena of interest are the emergence of topogical superlattice states, quantum interferences and excitonic interactions in weakly coupled nanostructures, as well as the interaction of single spins and photon emitters in hybrid arrays.

The potential of superlattice potentials

Exposition of electrons to superlattice potentials is an approach that has been extensively applied on conventional, spin-degenerated 2D surface electronic states for tuning their lateral confinement. By adding spin-momentum locking to surface electrons, novel spin-orbit flip scattering mechanisms emerge. According to theoretical predictions, in the presence of a superlattice potential such spin-orbit coupled (SOC) scattering may lead to anomalous anisotropic renormalization and electron collimation, similar to the effect of pseudospin-momentum locking in graphene. It can also cause electric-field controlled 1D spin wave texture, which can be further manipulated using terahertz radiation, or tunable anisotropic plasmon enhancement. Recently, the use of periodic potentials has been proposed as scaffold to engineer the topology of Rashba superconductors aiming at the generation of Majorana Fermions. Researchers at the ICN2 are exploring an innovative strategy of imprinting 1D superlattices with tunable periodicity to SOC-based quantum materials by using a fully bottom-up approach. This allows growing and characterizing the nanostructured materials in-situ and with atomic precision.

Quantum oxides

Oxides are known to display an enormous variety of physical properties, many of which are regarded as archetypes of solid-state quantum behaviour. These include high-temperature superconductivity or Mott metal-insulator transitions. The ICN2 Nanomaterials Growth division can count on state-of-the-art equipment for the growth of high quality oxide thin films, such as a multi-chamber RHEED-assisted pulsed laser deposition system and a multi-gun off-axis RF sputtering chamber. In turn, the Oxide Nanophysics group is expert in characterization of physical properties at the nanoscale and/or at low temperatures, by means of specific equipment, including a cryogenic Atomic Force Microscope (which can cool samples down to 4K and apply magnetic fields of up to 9T in-situ). Thanks to these facilities, researchers at the ICN2 are studying the Mott metal-insulator transition of VO2, which conveniently happens near room temperature, as well as 2D and topological structures within ferroics, such as ferroelectric domain walls and polar skyrmions.

Optoelectronic properties of quantum materials

At the ICN2, we study optoelectronic properties, such as the ultrafast charge dynamics, nonlinear optical properties and thermal transport properties, of quantum materials, in particular graphene and related 2D materials. We also aim to exploit these properties towards applications with novel/improved functionalities, such as: photodetection, nonlinear photonics and thermal management for ICT applications; and thermoelectrics and light harvesting for energy applications. To achieve this, we use state-of-the art techniques, some of which exploit (ultrafast) laser systems.

Selected references:

• Nat. Nanotechnol. published online (2021)
• ACS Nano 15, 11285–11295 (2021)
• Nanoscale 13, 8376 (2021)
• Sci. Adv. 7, eabf9809 (2021)
• Sci. Adv. 7, eabd9061 (2021)
• ACS Nano 15, 1145 – 1154(2021)
• Nat. Commun. 11, 4094 (2020)
• Nature 561, 507 (2018)

2D materials

Advances in 2D and layered materials are particularly attractive due to their potential high-performance as ultra-flat thermoelectric materials. Their atomically thin nature and extraordinary electrical, thermal, and acoustic properties, among others, have positioned them in the roadmap of potential future electronic and energy devices. Currently, research in quantum 2D materials includes topological insulators as well as already established thermoelectric materials that exhibit high thermoelectric performance and robust surface states, such as Bi₂Te₃, Sb₂Te₃, and Bi₂Se₃. Materials such as graphene, MoS₂, PtSe₂, WSe₂ and 2D heterostructures are being investigated.