Exploring Novel Electronic Structures of Topological Quantum Matter
Lead Research Organisation:
University of Oxford
Department Name: Oxford Physics
Abstract
Electronic materials play a tremendous role in almost every aspect of modern life - from supercomputers to household electronics - and the behavior of electrons in these materials determines their rich and unusual properties. Historically, the discoveries of novel electronic quantum materials have caused revolutions in our lifestyle and economy, such as the discovery of semiconductors. Very recently, an entirely new type of electronic materials, the topological insulator, was theoretically predicted and experimentally realized.
Topological insulators represent a brand new state of quantum matter that is distinct to ALL previously known states. On the face of it, they are well-known, off the shelf materials; but they have profound, yet previously overlooked properties that make them so unique. In its pure form, a topological insulator has a full energy gap in the bulk electron band (thus like an insulator); while on the surface, it has metallic states formed by electrons with linear energy-momentum relationship (similar to photons that do not possess rest mass!) with their spin polarization completely determined by their moving directions. More dramatically, these unusual electrons are extremely robust, and can flow on the surface of topological insulators against any non-magnetic impurities, crystalline defects or surface distortions. Due to the great scientific significance and technological potential, topological insulators have grown as one of the most intensely studied fields in condensed matter physics within the last few years.
However, while the scientists worldwide are advancing the frontier of this exciting field, there remain many challenges before we can actually realize the many amazing quantum phenomena (such as the magnetic monopoles, half electron charge and many topological magneto-electric effects resulted from the revised Maxwell equations in topological insulators) and practical applications (such as novel electronic, spintronic and thermoelectric applications) topological insulators promise. For examples, current topological insulators typically have excessive bulk carriers, thus prevent the bulk from being insulating (which will mask the subtle topological effects from the surface electrons); and the small bulk energy gap also prevent them from being used in high (room) temperature electronic devices. Thus we would like to solve these problems by carrying out this project to improve the quality of current topological insulators, and search for even better topological insulators with larger bulk energy gap and more stable in regular environments. We will also explore the pathways to use the unusual electronic and spin properties of topological insulators in practical applications, such as ultra-low power electronics, novel spintronic devices, optoelectronic applications, high efficiency thermoelectric applications and catalysis applications.
Furthermore, the swift development of topological insulators has also inspired the study of other new topological states, such as quantum anomalous Hall insulators, topological semi-metals, topological crystalline insulators and topological superconductors, etc. These new topological states will unlock the door to even richer exotic quantum phenomena (such as quantized Hall conductance without externally applied magnetic field, and the exotic Majorana fermions that are their own anti-particles) and more unconventional applications (from ultra-low integrate circuit to future topological quantum computers) Thus we will also search for these novel phases of quantum matter in this project.
Topological insulators represent a brand new state of quantum matter that is distinct to ALL previously known states. On the face of it, they are well-known, off the shelf materials; but they have profound, yet previously overlooked properties that make them so unique. In its pure form, a topological insulator has a full energy gap in the bulk electron band (thus like an insulator); while on the surface, it has metallic states formed by electrons with linear energy-momentum relationship (similar to photons that do not possess rest mass!) with their spin polarization completely determined by their moving directions. More dramatically, these unusual electrons are extremely robust, and can flow on the surface of topological insulators against any non-magnetic impurities, crystalline defects or surface distortions. Due to the great scientific significance and technological potential, topological insulators have grown as one of the most intensely studied fields in condensed matter physics within the last few years.
However, while the scientists worldwide are advancing the frontier of this exciting field, there remain many challenges before we can actually realize the many amazing quantum phenomena (such as the magnetic monopoles, half electron charge and many topological magneto-electric effects resulted from the revised Maxwell equations in topological insulators) and practical applications (such as novel electronic, spintronic and thermoelectric applications) topological insulators promise. For examples, current topological insulators typically have excessive bulk carriers, thus prevent the bulk from being insulating (which will mask the subtle topological effects from the surface electrons); and the small bulk energy gap also prevent them from being used in high (room) temperature electronic devices. Thus we would like to solve these problems by carrying out this project to improve the quality of current topological insulators, and search for even better topological insulators with larger bulk energy gap and more stable in regular environments. We will also explore the pathways to use the unusual electronic and spin properties of topological insulators in practical applications, such as ultra-low power electronics, novel spintronic devices, optoelectronic applications, high efficiency thermoelectric applications and catalysis applications.
Furthermore, the swift development of topological insulators has also inspired the study of other new topological states, such as quantum anomalous Hall insulators, topological semi-metals, topological crystalline insulators and topological superconductors, etc. These new topological states will unlock the door to even richer exotic quantum phenomena (such as quantized Hall conductance without externally applied magnetic field, and the exotic Majorana fermions that are their own anti-particles) and more unconventional applications (from ultra-low integrate circuit to future topological quantum computers) Thus we will also search for these novel phases of quantum matter in this project.
Planned Impact
In addition to the great scientific merit, the proposed study on topological quantum materials can also promote the technology advances and contribute to the economy growth. This work has the potential to impact on:
1. Ultra low power electronics: The suppression of backscattering of the edge/surface states in topological insulators (Science, 318/766, 2007) corresponds to exceptional transport mobility and reduced energy consumption, which is extremely attractive for semiconductor devices.
2. Novel spintronic devices: In addition to their great potential in electronic devices, topological insulators are also attractive for future spintroinc applications. The well-defined correlation between the electron motion and its spin direction in topological insulators (Science, 323/919, 2009) enables the direct control of spin current by electric current. Also, the generation of a magnetic monopole by a pure electric charge can support novel all electric read/write head for future hard drives.
3. Optoelectronics: This is also an emerging area for topological insulators applications. Our discovery of the excellent optical transparency and electric conductivity (Nature Chem. 4/281, 2012) makes topological insulator thin films ideal candidates for flexible transparent electrodes.
4. High efficiency thermoelectric applications: Almost all currently known topological insulators are good thermoelectric materials. Further improvement on thermoelectric efficiency can be achieved by nano-engineering such as fabrication of nano-structured composites, in which the electric conductivity remains excellent (due to the enhanced surface area) while the thermal conductivity is diminished (due to the vast phonon scattering at the interfaces between nano-particles).
5. Catalysis applications: The robust surface states of topological insulators can provide a stable electron bath for effecting surface reactions, thus can serve as supports for various catalysts (e.g. Phys. Rev. Lett. 107/056804, 2011).
And the beneficiaries will be:
1. Semiconductor industries (Integrated circuit companies, optoelectric companies, consumer electronics companies)
2. Energy industry (High efficiency thermoelectric generators,)
3. Space exploration research institute (e.g. Nuclear-thermoelectric batteries used in satellites and Mars' rovers)
4. Consumer appliance industry (e.g. thermal electric heater/cooler)
5. Materials and chemistry industry (e.g. using topological quantum materials as catalysis)
1. Ultra low power electronics: The suppression of backscattering of the edge/surface states in topological insulators (Science, 318/766, 2007) corresponds to exceptional transport mobility and reduced energy consumption, which is extremely attractive for semiconductor devices.
2. Novel spintronic devices: In addition to their great potential in electronic devices, topological insulators are also attractive for future spintroinc applications. The well-defined correlation between the electron motion and its spin direction in topological insulators (Science, 323/919, 2009) enables the direct control of spin current by electric current. Also, the generation of a magnetic monopole by a pure electric charge can support novel all electric read/write head for future hard drives.
3. Optoelectronics: This is also an emerging area for topological insulators applications. Our discovery of the excellent optical transparency and electric conductivity (Nature Chem. 4/281, 2012) makes topological insulator thin films ideal candidates for flexible transparent electrodes.
4. High efficiency thermoelectric applications: Almost all currently known topological insulators are good thermoelectric materials. Further improvement on thermoelectric efficiency can be achieved by nano-engineering such as fabrication of nano-structured composites, in which the electric conductivity remains excellent (due to the enhanced surface area) while the thermal conductivity is diminished (due to the vast phonon scattering at the interfaces between nano-particles).
5. Catalysis applications: The robust surface states of topological insulators can provide a stable electron bath for effecting surface reactions, thus can serve as supports for various catalysts (e.g. Phys. Rev. Lett. 107/056804, 2011).
And the beneficiaries will be:
1. Semiconductor industries (Integrated circuit companies, optoelectric companies, consumer electronics companies)
2. Energy industry (High efficiency thermoelectric generators,)
3. Space exploration research institute (e.g. Nuclear-thermoelectric batteries used in satellites and Mars' rovers)
4. Consumer appliance industry (e.g. thermal electric heater/cooler)
5. Materials and chemistry industry (e.g. using topological quantum materials as catalysis)
Organisations
People |
ORCID iD |
| Yulin Chen (Principal Investigator) |
Publications
Chen Y
(2013)
Discovery of a single topological Dirac fermion in the strong inversion asymmetric compound BiTeCl
in Nature Physics
Liu ZK
(2014)
A stable three-dimensional topological Dirac semimetal Cd3As2.
in Nature materials
Liu ZK
(2016)
Evolution of the Fermi surface of Weyl semimetals in the transition metal pnictide family.
in Nature materials
Liu ZK
(2014)
Discovery of a three-dimensional topological Dirac semimetal, Na3Bi.
in Science (New York, N.Y.)
Narayanan A
(2015)
Linear magnetoresistance caused by mobility fluctuations in n-doped Cd(3)As(2).
in Physical review letters
Shekhar C
(2015)
Extremely large magnetoresistance and ultrahigh mobility in the topological Weyl semimetal candidate NbP
in Nature Physics
Watson M
(2015)
Emergence of the nematic electronic state in FeSe
Watson M
(2015)
Emergence of the nematic electronic state in FeSe
in Physical Review B
Yang H
(2018)
Single crystalline electronic structure and growth mechanism of aligned square graphene sheets
in APL Materials
| Description | During the award period, we discovered i) The first strongly inversion asymmetric topological insulator, which may not only lead to many interesting phenomena, such as crystalline-surface-dependent topological electronic states, pyroelectricity and intrinsic topological p-n junctions, but would also serve as an ideal platform for the realization of topological magneto-electric effects. ii) First 3D topological Dirac semimetal (TDS) Na3Bi, which is a natural 3D counterpart of graphene. The distinct electronic structure of a TDS not only makes it possible to realize some exciting phenomena and applications of graphene in 3D materials, but also makes it an ideal platform for the systematic study of quantum phase transitions between rich topological quantum states, including topological weyl semimetals, Axion Insulators and topological superconductors. iii) After the discovery of Na3Bi, we discovered the first stable 3D TDS Cd3As2. In addition to its stability in ambient environment, electrons in Cd3As2 have much higher Fermi velocities, making it a better candidate material for practical applications. iv)First topological Weyl semimetal TaAs. We not only discovered the elusive Weyl fermions in the electronic structure of this material, but also observed the unique "Fermi-arcs" which are the Fermi-surface comprised of exotic open curves. v) The Fermiology evolution in the transition metal pnictide family of Weyl semimetals and revealed the mechanism to realize and fine-tune the electronic structures of topological Weyl semimetals, which provide a rich material base for exploring many exotic physical phenomena and novel future applications |
| Exploitation Route | Our finding of these new topological quantum materials no only provides ideal platforms for the discovery of new states of matter and many intriguing physical phenomena, but also makes various novel applications (in electronics, spintronics and optoelectronic and thermoelectric devices) possible. |
| Sectors | Aerospace, Defence and Marine,Digital/Communication/Information Technologies (including Software),Electronics |
| URL | http://www.nature.com/news/wonders-of-flat-physics-now-seen-in-3d-1.14538 |
| Description | The funding is used for the following purpose and activities: 1) Contribute 10% of my time (with another 10% matched by the department) for this project. 2) Purchase chemicals for sample synthesis 3) Purchase necessary lab tools, consumables and computer stations for data analysis 3) Support travels to conduct experiments in external user facilities (e.g. Stanford Synchrotron Light Source, Advanced Light Source in Lawrence Berkeley National Lab in USA, Elettra Synchroton in Italy) 4) Support travels to attend international conferences (e.g. APS March meeting, EMRS meeting, International Conference on Crystal Growth and Epitaxy, etc.) to publicize our research results and discuss with other experts in the field. 5) Support our collaborators' trips to Oxford (for scientific discussion, joining our experiments at Diamond synchrotron and developing samples locally). 6) Cover the cost for using departmental shared facilities, such as X-ray lab, Mechanical workshop, PPMS, SQUID, etc. |
| First Year Of Impact | 2015 |
| Sector | Education,Electronics,Other |