Toward Quantum Devices as One Billionth of a Machine

Nano- and atomic-scale materials exhibit specific magnetic and ferroelectric properties and multiferroic functions that can interconvert mechanical, electrical and magnetic energy. The aim is to unravel this and create ’nano-quantum machines’, machines that can operate in the tiny world of ‘one hundred millionth of a billionth’.

Nanomachines in “One-Billionth” World by Lattice Defects

-Toward functional materials with quantum/atom scales-

In contrast to mascroscale structures, nanomachines, which are small machines (e.g., drug delivery to affected areas or nanomachines to repair damaged parts inside equipment), would be one of the dream machines. In order to create nanomachines, it is essential to have a mechanism that is ultimately small enough to move freely within the material to do the desired job.

We have discovered that lattice defects in crystals have functions such as ferroelectricity and magnetism that are not found in the host material, and that they can move freely within the material and perform a variety of useful tasks with respect to external fields. For example, atomic vacancies develop localised magnetism and ferroelectricity (multiferroics) of 1-2 nm and behave as ‘atomic-scale nanomachines’ that are mechanically driven by external electric and magnetic fields, dislocation aggregates with multiferroic functions can function as ‘atomic-scale logic operation circuits’ such as AND and NOR. The discovery that grain boundaries can be used as atomic-thickness multiferroic thin films for storage devices, etc., all overturned what had been thought to be impossible according to conventional wisdom.

Related Publication

• Takahiro Shimada, Jie Wang, Taku Ueda, Yoshitaka Uratani, Kou Arisue, Matous Mrovec, Christian Elsässer, Takayuki Kitamura
  Multiferroic grain boundaries in oxygen-deficient ferroelectric lead titanate
  Nano Letters, 15, 27 (2015)

• Takahiro Shimada, Jie Wang, Yoshimitsu Araki, Matous Mrovec, Christian Elsässer, Takayuki Kitamura
  Multiferroic vacancies at ferroelectric PbTiO₃ surfaces
  Physical Review Letters, 115, 107202 (2015)

• Tao Xu, Takahiro Shimada, Yoshimitsu Araki, Jie Wang, Takayuki Kitamura
  Multiferroic domain walls in ferroelectric PbTiO₃ with oxygen deficiency
  Nano Letters, 16, 454 (2016)

• Takahiro Shimada, Tao Xu, Yoshimitsu Araki, Jie Wang, Takayuki Kitamura
  Multiferroic dislocations in ferroelectric PbTiO₃
  Nano Letters, 17, 2674 (2017)

Diverse Physical Properties in a Ultrasmall Dimensions

“There is plenty of room at the bottom”
- Prof. Richard P. Feynman

Many material properties have been thought of as “material constants” that are uniquely determined by the composition and structure of the material. However, materials on the nanometer (billionth of a meter) scale, even if they have the same composition, have properties that are completely different from those we are familiar with in the macroscopic world. For example, we have discovered that chiral nanotube structures, such as carbon nanotubes, exhibit magnetic and ferroelectric properties that are also characteristic of helical structures. We are contributing to the improvement of functions of electronic devices and micro/nano-machines by structurally designing microscopic material properties through the clarification of the “correlation between structure and function” laws in such a small world.

Related Publication

• Takahiro Shimada, Xiaoyuan Wang, Yoshihiro Kondo, Takayuki Kitamura
  Absence of ferroelectric critical size in ultrathin PbTiO₃ nanotubes: A density-functional theory study
  Physical Review Letters, 108, 067601 (2012)

• Takahiro Shimada, Junichi Okuno, Takayuki Kitamura
  Chiral selectivity of unusual helimagnetic transition in iron nanotubes: Chirality makes quantum helimagnets
  Nano Letters, 13, 2792 (2013)

• Takahiro Shimada, Tao Xu, Yoshitaka Uratani, Jie Wang, Takayuki Kitamura
  Unusual multiferroic phase transitions in PbTiO₃ nanowires
  Nano Letters, 16, 6774 (2016)

• Tao Xu, Takahiro Shimada, Yoshitaka Uratani, Xiaoyuan Wang, Jie Wang, Takayuki Kitamura
  Multiferroic phases and transitions in ferroelectric lead titanate nanodots
  Scientific Reports, 7, 45373 (2017)